22 Nov24
Title: Strong constraints on a sharp change in $G$ as a solution to the Hubble tension
Authors: Indranil Banik, Harry Desmond and Nick Samaras
https://arxiv.org/pdf/2411.15301
.pdf
Abstract:
It has been proposed that if the gravitational constant $G$ abruptly
decreased around 130 Myr ago, then Type Ia supernovae (SNe) in the Hubble flow
would have a different luminosity to those in host galaxies with Cepheid
distances. This would make Hubble flow SNe more distant, causing redshifts to
rise slower with distance, potentially solving the Hubble tension. We find that
since the luminosities of Sun-like stars scale as approximately $G^7$, the
Solar luminosity would have dropped substantially 130 Myr ago in this scenario,
pushing Earth into a planetary glaciation. However, there was no Snowball Earth
episode in the last 500 Myr. The $G$ step model (GSM) also implies that the
length of a year would have abruptly increased by about 10%, but the number of
days per year has evolved broadly continuously according to geochronometry and
cyclostratigraphy. The GSM would drastically alter stellar evolution, causing
the Sun to have exhausted about 2/3 of its fuel supply rather than 1/2. This
would lead to the helioseismic age of the Sun differing from that of the oldest
meteorite samples, but these agree excellently in practice. There is also
excellent agreement between the standard expansion history and that traced by
cosmic chronometers, but these would disagree severely in the GSM. Moreover,
distance indicators that use stellar luminosities would differ drastically
beyond 40 Mpc from those that do not. These arguments cast very severe doubt on
the viability of the GSM: the solution to the Hubble tension must be sought
elsewhere.
Title: Impacts of UV Radiation from an AGN on Planetary Atmospheres and
Consequences for Galactic Habitability
Authors: Kendall I. Sippy, Jake K. Eager-Nash, Ryan C. Hickox, Nathan J. Mayne,
McKinley C. Brumback
https://arxiv.org/pdf/2411.15341
.pdf
Abstract:
We present a study of the effects of ultraviolet (UV) emission from active
galactic nuclei (AGN) on the atmospheric composition of planets and potential
impact on life. It is expected that all supermassive black holes, which reside
at galactic centers, have gone through periods of high AGN activity in order to
reach their current masses. We examine potential damaging effects on lifeforms
on planets with different atmosphere types and receiving different levels of
AGN flux, using data on the sensitivity of various species' cells to UV
radiation to determine when radiation becomes ``dangerous''. We also consider
potential chemical changes to planetary atmospheres as a result of UV radiation
from AGN, using the PALEO photochemical model. We find the presence of
sufficient initial oxygen (surface mixing ratio $\geq 10^{-3} \rm\, mol/mol$)
in the planet's atmosphere allows a thicker ozone layer to form in response to
AGN radiation, which reduces the level of dangerous UV radiation incident on
the planetary surface from what it was in absence of an AGN. We estimate the
fraction of solar systems in galaxies that would be affected by AGN UV
radiation, and find that the impact is most pronounced in compact galaxies such
as ``red nugget relics'', as compared to typical present-day ellipticals and
spirals (using M87 and the Milky Way as examples). Our work generally supports
the Gaia hypothesis, where the development of life on a planet (and resulting
oxygenation of the atmosphere) causes the environment to become more stable
against potential extinction events in the future.
Title: 4FGL J1544.2$-$2554: a new spider pulsar candidate
Authors: A. V. Karpova, S. V. Zharikov, D. A. Zyuzin, A. Yu. Kirichenko, Yu. A.
Shibanov, I. F. M\'arquez
https://arxiv.org/pdf/2411.16350
.pdf
Abstract:
Context. Spider pulsars are millisecond pulsars in tight binary systems, in
which a low-mass companion star is heated and ablated by the pulsar wind. Their
observations allow one to study stellar evolution with formation of millisecond
pulsars and physics of superdense matter in neutron stars. However, spiders are
rare due to difficulties of their discovery using typical radio search
techniques. The Fermi $\gamma$-ray source 4FGL J1544.2$-$2554 was recently
proposed as a pulsar candidate, and its likely X-ray and optical counterparts
with the galactic coordinates $l\approx344.\!\!^\circ76$,
$b\approx22.\!\!^\circ59$ and the magnitude $G\approx20.6$ were found using the
eROSITA and Gaia surveys. Aims. Our goals are to study whether the source is a
new spider pulsar and to estimate its fundamental parameters. Methods. We
performed the first optical time-series multi-band photometry of the object. We
used the Lomb-Scargle periodogram to search for its brightness periodicity and
fitted its light curves with a model of direct heating of the binary companion
by the pulsar wind. Results. The source shows a strong brightness variability
with a period of $\approx$ 2.724 h and an amplitude of $\gtrsim$ 2.5 mag, and
its light curves have a single broad peak per period. These features are
typical for spider pulsars. The curves are well fitted by the direct heating
model, resulting in an orbit inclination of the presumed spider system of
$\approx 83^\circ$, a companion mass of $\approx 0.1$ M$_\odot$, its
''day-side'' and ''night-side'' temperatures of $\approx 7200$ K and $\approx
3000$ K, a Roche-lobe filling factor of $\approx 0.65$ and a distance of
$\approx 2.1$ kpc. Conclusions. Our findings suggest that 4FGL J1544.2$-$2554
is a spider pulsar. This encourages searches for the pulsar millisecond
pulsations in the radio and $\gamma$-rays to confirm its nature.
Title: The perils of stacking optically selected groups in eROSITA data. The
Magneticum perspective
Authors: P. Popesso, I. Marini, K. Dolag, G. Lamer, B. Csizi, S.
Vladutescu-Zopp, V. Biffi, A. Robothan, M. Bravo, E. Tempel, X. Yang, Q. Li,
A. Biviano, L. Lovisari, S. Ettori, M. Angelinelli, S. Driver, V. Toptun, A.
Dev, D. Mazengo, A. Merloni, J. Comparat, Y. Zhang, G. Ponti, and E. Bulbul
https://arxiv.org/pdf/2411.16546
.pdf
Abstract:
Hydrodynamical simulation predictions are often compared with observational
data without fully accounting for systematics and biases specific to
observational techniques. Using the magnetohydrodynamical simulation
Magneticum, we generate mock eROSITA eRASS:4 data, combined with GAMA-like
spectroscopic surveys and optically selected galaxy catalogs from the same
light-cone, to analyze hot gas properties in galaxy groups via a stacking
technique. This study aims to (i) incorporate observational systematics into
predictions and (ii) evaluate the reliability of stacking techniques for
determining average X-ray properties of galaxy groups. Our analysis provides
X-ray emission predictions from Magneticum, including contributions from AGN,
X-ray binaries (XRBs), and the Intra-Group Medium (IGM) as a function of halo
mass, covering Milky Way (MW)-like groups to poor clusters. We find that AGN
and XRBs dominate the X-ray surface brightness profiles of low-mass halos. The
reliability of stacking techniques is tested by reproducing input X-ray surface
brightness and electron density profiles, accounting for completeness and
contamination of prior samples, miscentering of optical group centers,
uncertainties in X-ray emissivity due to gas temperature and metallicity
assumption, and systematics in halo mass proxies. The halo mass proxy emerges
as the primary source of systematics, affecting X-ray surface brightness and
scaling relations. We show that stacked X-ray luminosity-mass relations are
flatter than input relations but consistent with observations. Additionally,
the retrieved hot gas fraction-mass relation aligns well with observational
data. These results highlight the need to account for systematic errors when
comparing stacking techniques to other methods using different prior catalogs
or predictions.
21 Nov24
Title: Understanding Stellar Mass-Metallicity and Size Relations in Simulated Ultra-Faint Dwarf Galaxies
Authors: Minsung Ko, Myoungwon Jeon, Yumi Choi, Nitya Kallivayalil, Sangmo Tony
Sohn, Gurtina Besla, Hannah Richstein, Sal Wanying Fu, Tae Bong Jeong, Jihye
Shin
https://arxiv.org/pdf/2411.14683
.pdf
Abstract:
Reproducing the physical characteristics of ultra-faint dwarf galaxies (UFDs)
in cosmological simulations is challenging, particularly with respect to
stellar metallicity and galaxy size. To investigate these difficulties in
detail, we conduct high-resolution simulations ($M_{\rm gas} \sim 60 \,
M_{\odot}$, $M_{\rm DM} \sim 370 \, M_{\odot}$ ) on six UFD analogs ($M_{\rm
vir} \sim 10^8 - 10^9 \, M_{\odot}$, $M_{\rm \star} \sim 10^3 - 2.1 \times 10^4
\, M_{\odot}$). Our findings reveal that the stellar properties of UFD analogs
are shaped by diverse star-forming environments from multiple progenitor halos
in the early Universe. Notably, our UFD analogs exhibit a better match to the
observed mass-metallicity relation (MZR), showing higher average metallicity
compared to other theoretical models. The metallicity distribution functions
(MDFs) of our simulated UFDs lack high-metallicity stars ($[\rm Fe/H] > -2.0$)
while containing low-metallicity stars ($[\rm Fe/H] < -4.0$). Excluding these
low-metallicity stars, our results align well with the MDFs of observed UFDs.
However, forming stars with higher metallicity ($-2.0 \leq [\rm Fe/H]_{\rm max}
\leq -1.5$) remains a challenge due to the difficulty of sustaining metal
enrichment during their brief star formation period before cosmic reionization.
Additionally, our simulations show extended outer structures in UFDs, resulting
from dry mergers between progenitor halos. To ensure consistency, we adopt the
same fitting method commonly used in observations to derive the half-light
radius. We find that this method tends to produce lower values compared to
direct calculations and struggles to accurately describe the extended outer
structures. To address this, we employ a two-component density profile to
obtain structural parameters, finding that it better describes the galaxy
shape, including both inner and outer structures.
Title: Untangling Magellanic Streams
Authors: Dennis Zaritsky, Vedant Chandra, Charlie Conroy, Ana Bonaca, Phillip
A. Cargile, Rohan P. Naidu
https://arxiv.org/pdf/2411.15044
.pdf
Abstract:
The Magellanic Stream has long been known to contain multiple HI strands and
corresponding stellar populations are beginning to be discovered. Combining an
H3-selected sample with stars drawn from the Gaia catalog, we trace stars along
a sub-dominant strand of the Magellanic Stream, as defined by gas content,
across 30$^\circ$ on the sky. We find that the dominant strand is devoid of
stars with Galactocentric distance $\lesssim 55$ kpc while the subdominant
strand shows a close correspondence to such stars. We conclude that (1) the two
Stream strands have different origins, (2) they are likely only close in
projection, (3) the subdominant strand is tidal in origin, and (4) the
subdominant strand is composed of disk material, likely drawn from the disk of
the Small Magellanic Cloud.
20 Nov24
Title: Radial Metallicity Gradients for the Chemically Selected Galactic Thin Disc Main-Sequence Stars
Authors: F. Akbaba, T. Ak, S. Bilir, O. Plevne, Onal Tas. O, G. M. Seabroke
https://arxiv.org/pdf/2411.13660
.pdf
Abstract:
{We present the radial metallicity gradients within the Galactic thin disc
population through main-sequence stars selected on the chemical plane using
GALAH DR3 accompanied with Gaia DR3 astrometric data. The [Fe/H], [$\alpha$/Fe]
and [Mg/H] radial gradients are estimated for guiding radius as $-0.074\pm
0.006$, $+0.004\pm0.002$, $-0.074\pm0.006$ dex kpc$^{-1}$ and for the traceback
early orbital radius as $-0.040\pm0.002$, $+0.003\pm 0.001$, $-0.039\pm 0.002$
dex kpc$^{-1}$ for 66,545 thin-disc stars, respectively. Alteration of the
chemical structure within the Galactic disc caused by the radial orbital
variations complicates results for the radial metallicity gradient. The effect
of radial orbital variations on the metallicity gradients as a function on time
indicates the following results: (i) The presence of a gradient along the disc
throughout the time for which the model provides similar prediction, (ii) the
radial orbital variations becomes more pronounced with the age of the stellar
population and (iii) the effect of radial orbital variations on the metallicity
gradients is minimal. The effect of radial orbital variations is found to be at
most 6\% which does not statistically affect the radial gradient results. These
findings contribute to a better understanding of the chemical evolution within
the Galactic disc and provide an important basis for further research.
Title: X-Shooting ULLYSES: Massive Stars at Low Metallicity X. Physical
Parameters and Feedback of Massive Stars in the LMC N11 B Star-Forming Region
Authors: V.M.A. G\'omez-Gonz\'alez, L.M. Oskinova, W.-R. Hamann, H. Todt, D.
Pauli, S. Reyero Serantes, M. Bernini-Peron, A.C. Sander, V. Ramachandran,
J.S. Vink, P.A. Crowther, S.R. Berlanas, A. ud-Doula, A.C. Gormaz-Matamala,
C. Kehrig, R. Kuiper, C. Leitherer, L. Mahy, A.F. McLeod, A. Mehner, N.
Morrell, T. Shenar, O.G. Telford, J. Th. van Loon, F. Tramper, A. Wofford
https://arxiv.org/pdf/2411.14149
.pdf
Abstract:
Massive stars lead the ionization and mechanical feedback within young
star-forming regions. The Large Magellanic Cloud (LMC) is an ideal galaxy for
studying individual massive stars and quantifying their feedback contribution
to the environment. We analyze eight exemplary targets in LMC N11 B from the
Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES)
program, using novel spectra from HST (COS and STIS) in the UV, and from VLT
(X-shooter) in the optical. We model the spectra of early to late O-type stars
by using state-of-the-art PoWR atmosphere models. We determine the stellar and
wind parameters (e.g., $T_\star$, $\log g$, $L_{\star}$, $\dot{M}$, $v_\infty$)
of the analyzed objects, chemical abundances (C, N, O), ionizing and mechanical
feedback ($Q_\mathrm{H}$, $Q_\mathrm{He{\small{I}}}$,
$Q_\mathrm{He{\small{II}}}$, $L_\mathrm{mec}$) and X-rays. We report ages of
$2-4.5$ Myr and masses of $30-60$ $M_\odot$ for the analyzed stars in N11 B,
consistent with a scenario of sequential star formation. We note that the
observed wind-momentum luminosity relation is consistent with theoretical
predictions. We detect nitrogen enrichment in most of the stars, up to a factor
of seven. However, we do not find a correlation between nitrogen enrichment and
projected rotational velocity. Finally, based on their spectral type, we
estimate the total ionizing photons injected from the O-type stars in N11 B
into its environment. We report $\log$ ($\sum$ $Q_\mathrm{H}$)$=50.5$ ph
s$^{-1}$, $\log$ ($\sum$ $Q_\mathrm{He{\small{I}}}$)$=49.6$ ph s$^{-1}$ and
$\log$ ($\sum$ $Q_\mathrm{He{\small{II}}}$)$=44.4$ ph s$^{-1}$, consistent with
the total ionizing budget in N11.
Title: Constraining the Binarity of Massive Black Holes in the Galactic Center
and Some Nearby Galaxies via Pulsar Timing Array Observations of
Gravitational Waves
Authors: Xiao Guo, Qingjuan Yu, and Youjun Lu
https://arxiv.org/pdf/2411.14150
.pdf
Abstract:
Massive black holes (MBHs) exist in the Galactic center (GC) and other nearby
galactic nuclei. As natural outcome of galaxy mergers, some MBHs may have a
black hole (BH) companion. In this paper, assuming that the MBHs in the GC and
some nearby galaxies are in binaries with orbital periods ranging from months
to years (gravitational-wave frequency $\sim1-100$\,nHz), we investigate the
detectability of gravitational-waves from these binary MBHs (BBHs) and
constraints on the parameter space for the existence of BBHs in the GC, LMC,
M31, M32, and M87, that may be obtained by current/future pulsar timing array
(PTA) observations. We find that a BBH in the GC, if any, can be revealed by
the Square Kilometer Array PTA (SKA-PTA) if its mass ratio
$q\gtrsim10^{-4}-10^{-3}$ and semimajor axis $a\sim20-10^3$\,AU. The existence
of a BH companion of the MBH can be revealed by SKA-PTA with $\sim20$-year
observations in M31 if $q\gtrsim10^{-4}$ and $a\sim10^2-10^4$\,AU or in M87 if
$q\gtrsim10^{-5}$ and $a\sim10^3-2\times10^4$\,AU, but not in LMC and M32 if
$q\ll1$. If a number of milli-second stable pulsars with distances
$\lesssim0.1-1$\,pc away from the central MBH in the GC, LMC, M32, or M31, can
be detected in future and applied to PTAs, the BH companion with mass even down
to $\sim100M_\odot$, close to stellar masses, can be revealed by such PTAs.
Future PTAs are expected to provide an independent way to reveal BBHs and
low-mass MBH companions in the GC and nearby galaxies, improving our
understandings of the formation and evolution of MBHs and galaxies.
Title: Examining the evolution of the Supersoft X-ray Source RX J$0513.9-6951$
Authors: A. Tavleev, V. F. Suleimanov, K. Werner, A. Santangelo
https://arxiv.org/pdf/2411.14273
.pdf
Abstract:
Supersoft X-ray sources (SSS) are thought to be accreting white dwarfs (WDs)
in close binary systems, with thermonuclear burning on their surfaces. The SSS
RX J$0513.9-6951$ in the Large Magellanic Cloud (LMC) exhibits cyclic
variations between optical low and high states, which are anti-correlated with
its X-ray flux. This behaviour is believed to result from the periodic
expansion and contraction of the WD due to variations in the accretion rate in
the system. We analyse eight high-resolution XMM and six grating Chandra
spectra of RX J$0513.9-6951$ with our grid of model atmosphere spectra of hot
WDs computed under the assumption of local thermodynamic equilibrium. Our aim
is to test a contraction model of the source variability by tracking the
evolution of the WD properties. The used grid of hot WD model atmospheres spans
a wide range of effective temperatures ($T_{\rm eff}=100-1000\,\rm kK$ in steps
of $25\,\rm kK$) and eight values of surface gravity $\log g$. The LMC chemical
composition was assumed. The obtained fitting parameters ($T_{\rm eff}$, $\log
g$, and bolometric luminosity $L$) evolve on the $T_{\rm eff}- \log g$ and
$T_{\rm eff}- L$ planes. This evolution follows the model tracks of WDs with
masses of $1.05-1.15\,M_{\odot}$ and thermonuclear burning on the surface. The
analysis has showed that the optical brightness of the system is lower when the
WD is larger, more luminous, and more effectively illuminates the accretion
disc. These results contradict the contraction model, which predicts the
opposite behaviour of the source. We use a model, that assumes that the far
UV/soft X-ray flux is reprocessed into the optical band due to multiple
scattering in the cloud system above the accretion disc. More significant
illumination can lead to rarefying of the cloud slab, thereby reducing the
reprocessing efficiency and making the source fainter in the optical band.
Title: Underestimation of Hubble constant error bars: a historical analysis
Authors: Martin Lopez-Corredoira
https://arxiv.org/pdf/2411.13621 (*cross-listing*)
.pdf
Abstract:
An analysis of a historical compilation of Hubble-Lema\^itre constant values
($H_0$: 163 data points measured between 1976 and 2019) assuming the standard
cosmological model gives a $\chi^2$ value of the dispersion with respect to the
weighted average of 580, much larger than the number of points, which has an
associated probability that is very low. This means that Hubble tensions were
always present in the literature, due either to the underestimation of
statistical error bars associated with the observed parameter measurements, or
to the fact that systematic errors were not properly taken into account in many
of the measurements.
The fact that the underestimation of error bars for $H_0$ is so common might
explain the apparent 4.4-sigma discrepancy by Riess et al. As a matter of fact,
more recent precise $H_0$ measurements with JWST data by Freedman et al. using
standard candles in galaxies find there is no tension with CMBR data, possibly
indicating that previously Riess et al. had underestimated their errors.
Here we have carried out a recalibration of the probabilities. The tension of
4.4-$\sigma $, estimated between the local Cepheid-supernova distance ladder
and cosmic microwave background (CMB) data, is indeed a 2.1-$\sigma $ tension
in equivalent terms of a normal distribution, with an associated probability
$P$ = 0.036 (1 in 28). This can be increased to an equivalent tension of
2.5-$\sigma $ in the worst cases of claimed 6-$\sigma $ tension, which may in
any case happen as a random statistical fluctuation.
If Hubble tensions were always present in the literature, and present day
tensions are not more important than previous ones, why, then, is there so much
noise and commotion surrounding Hubble tension after 2019? It is suggested here
that this obeys a sociological phenomenon of ``groupthink''.
19 Nov24
Title: Measuring the dipole component of possible Galaxy-binary alignment in the mHz band
Authors: Naoki Seto
https://arxiv.org/pdf/2411.12961
.pdf
Abstract:
We discuss the usability of the gravitational wave detector LISA for studying
the orientational distribution of compact white dwarf binaries in the Galactic
bulge. We pay special attention to measuring the dipole pattern of the
distribution around the Galactic rotation axis. Based on our new formulation,
which leverages the parity properties of the involved systems, we found that
the apparent thickness of the bulge in the sky becomes critical for the dipole
measurement. We also discuss the extra-Galactic studies for black hole binaries
and neutron star binaries with BBO/DECIGO.
Title: Identifying the Galactic Substructures in 5D Space Using All-sky RR
Lyrae Stars in Gaia DR3
Authors: Shenglan Sun, Fei Wang, Huawei Zhang, Xiang-Xiang Xue, Yang Huang,
Ruizhi Zhang, Hans-Walter Rix, Xinyi Li, Gaochao Liu, Lan Zhang, Chengqun
Yang, Shuo Zhang
https://arxiv.org/pdf/2411.13122
.pdf
Abstract:
Motivated by the vast gap between photometric and spectroscopic data volumes,
there is great potential in using 5D kinematic information to identify and
study substructures of the Milky Way. We identify substructures in the Galactic
halo using 46,575 RR Lyrae stars (RRLs) from Gaia DR3 with the photometric
metallicities and distances newly estimated by Li et al. (2023). Assuming a
Gaussian prior distribution of radial velocity, we calculate the orbital
distribution characterized by the integrals of motion for each RRL based on its
3D positions, proper motions and corresponding errors, and then apply the
friends-of-friends algorithm to identify groups moving along similar orbits. We
have identified several known substructures, including Sagittarius (Sgr)
Stream, Hercules-Aquila Cloud (HAC), Virgo Overdensity (VOD),
Gaia-Enceladus-Sausage (GES), Orphan-Chenab stream, Cetus-Palca, Helmi Streams,
Sequoia, Wukong and Large Magellanic Cloud (LMC) leading arm, along with 18
unknown groups. Our findings indicate that HAC and VOD have kinematic and
chemical properties remarkably similar to GES, with most HAC and VOD members
exhibiting eccentricity as high as GES, suggesting that they may share a common
origin with GES. The ability to identify the low mass and spatially dispersed
substructures further demonstrates the potential of our method, which breaks
the limit of spectroscopic survey and is competent to probe the substructures
in the whole Galaxy. Finally, we have also identified 18 unknown groups with
good spatial clustering and proper motion consistency, suggesting more
excavation of Milky Way substructures in the future with only 5D data.
18 Nov24
Title: ZTF SN Ia DR2: An environmental study of Type Ia supernovae using host galaxy image decomposition
Authors: R. Senzel, K. Maguire, U. Burgaz, G. Dimitriadis, M. Rigault, A.
Goobar, J. Johansson, M. Smith, M. Deckers, L. Galbany, M. Ginolin, L.
Harvey, Y.-L. Kim, T. E. Muller-Bravo, P. Nugent, P. Rosnet, J. Sollerman, J.
H. Terwel, R. R. Laher, D. Reiley, B. Rusholme
https://arxiv.org/pdf/2411.11986
.pdf
Abstract:
The second data release of Type Ia supernovae (SNe Ia) observed by the Zwicky
Transient Facility has provided a homogeneous sample of 3628 SNe Ia with
photometric and spectral information. This unprecedented sample size enables us
to better explore our currently tentative understanding of the dependence of
host environment on SN Ia properties. In this paper, we make use of
two-dimensional image decomposition to model the host galaxies of SNe Ia. We
model elliptical galaxies as well as disk/spiral galaxies with or without
central bulges and bars. This allows for the categorisation of SN Ia based on
their morphological host environment, as well as the extraction of intrinsic
galaxy properties corrected for both cosmological and atmospheric effects. We
find that although this image decomposition technique leads to a significant
bias towards elliptical galaxies in our final sample of galaxies, the overall
results are robust. By successfully modelling 728 host galaxies, we find that
the photometric properties of SNe Ia found in disks and in elliptical galaxies,
correlate fundamentally differently with their host environment. We identified
strong linear relations between light-curve stretch and our model-derived
galaxy colour for both the elliptical (16.8$\sigma$) and disk (5.1$\sigma$)
subpopulations of SNe Ia. Lower stretch SNe Ia are found in redder
environments, which we identify as an age/metallicity effect. Within the
subpopulation of SNe Ia found in disk containing galaxies, we find a
significant linear trend (6.1$\sigma$) between light-curve stretch and
model-derived local $r$-band surface brightness, which we link to the
age/metallicity gradients found in disk galaxies. SN Ia colour shows little
correlation with host environment as seen in the literature. We identify a
possible dust effect in our model-derived surface brightness (3.3$\sigma$), for
SNe Ia in disk galaxies.
Title: The possible dual nature of the asteroid (12499) 1998 FR47
Authors: G. Borisov, N. Todorovic, E. Vchkova-Bebekovska, A. Kostov and G.
Apostolovska
https://arxiv.org/pdf/2411.11994
.pdf
Abstract:
We present the R-band lightcurves of the Flora family asteroid (12499) 1998
FR47, obtained in 2022 at two different astronomical sites: Bulgarian National
Astronomical Observatory Rozhen (MPC Code 071) and Astronomical Station
Vidojevica (MPC Code C89). The quadramodal lightcurves reveal a rotation period
of 6.172+/-0.003 h and an amplitude of about 0.44 mag. Using the lightcurve
inversion method, with the combination of our dense lightcurves and the sparse
data from Gaia DR3, we found the sidereal period, an indication of a retrograde
rotation of (12499) and its low-convex resolution shape. Nonetheless, the
unusual shape of the quadramodal lightcurve and its additional analysis reveals
two possible periods, 3.0834+/-0.0085 h and 4.1245+/-0.0151 h, making the
suspect that the asteroid might be a non-synchronised wide binary system.
Spectral analysis of the asteroid using data from the GAIA DR3 shows that it is
either an M- or an L-type object and maybe a piece of the first planetesimals
to form in the Solar System protoplanetary disk. On the other hand, (12499)'s
dynamical properties indicate a significantly shorter lifetime. The asteroid
lies exactly on the chaotic border of the 7:4 mean motion resonance with Mars
(7M:4), alternating between being in and out of it for almost 190 Myrs. During
200 Myrs of integration, (12499) visited other resonances in the Flora family,
but it never became a Near Earth Object (NEO). Additional integration of
fictive objects from the 7M:4 resonance showed a possibility of transportation
to the NEO region already at about 20 Myrs.
Title: A slow spin to win -- the gradual evolution of the proto-Galaxy to the
old disc
Authors: Akshara Viswanathan, Danny Horta, Adrian M. Price-Whelan, Else
Starkenburg
https://arxiv.org/pdf/2411.12165
.pdf
Abstract:
Observational studies are identifying stars thought to be remnants from the
earliest stages of the hierarchical mass assembly of the Milky Way, referred to
as the proto-Galaxy. We use red giant stars with kinematics and [$\alpha$/M]
and [M/H] estimates from Gaia DR3 data to investigate the relationship between
azimuthal velocity and metallicity, aiming to understand the transition from a
chaotic proto-Galaxy to a well-ordered, rotating (old) disc-like population. To
analyse the structure of the data in [M/H]-v$_\phi$ space for both high- and
low-$\alpha$ samples with carefully defined $\alpha$-separation, we develop a
model with two Gaussian components in v$_\phi$: one representing a disc-like
population and the other a halo-like population. This model is designed to
capture the conditional distribution P(v$_\phi$ $\mid$ [M/H]) with a
2-component Gaussian Mixture Model with fixed azimuthal velocities means and
standard deviations. To quantify the spin-up of the high-$\alpha$ disc
population, we extend this two-component model by allowing the mean velocity
and velocity dispersion to vary between the spline knots across the metallicity
range used. We also compare our findings with existing literature using
traditional Gaussian Mixture Modelling in bins of [M/H] and investigate using
orbital circularity instead of azimuthal velocity. Our findings show that the
metal-poor high-$\alpha$ disc gradually spins up across [M/H] $\sim$ -1.7 to
-1.0, while the low-$\alpha$ sample exhibits a sharp transition at [M/H] $\sim$
-1.0. This latter result is due to the accreted debris dominating the
metal-poor end, underscoring the critical role of [$\alpha$/M] selection in
studying the (old) disc evolution of the Milky Way. These results indicate that
the proto-Galaxy underwent a slow, monotonic spin-up phase rather than a rapid,
dramatic spin-up at [M/H] $\sim$ -1.0, as previously inferred.
Title: RR Lyrae Stars in Intermediate-age Magellanic Clusters: Membership
Probabilities and Delay Time Distribution
Authors: Bolivia Cuevas-Otahola, Cecilia Mateu, Ivan Cabrera-Ziri, Gustavo
Bruzual, Fabiola Hern\'andez-P\'erez, Gladis Magris, Holger Baumgardt
https://arxiv.org/pdf/2411.12741
.pdf
Abstract:
Recent works have challenged our canonical view of RR Lyrae (RRL) stars as
tracers of exclusively old populations ($\gtrsim10$~Gyr) by proposing a
fraction of these stars to be of intermediate ages ($\sim$2-5~Gyr). Since it is
currently not possible to infer stellar ages directly for individual RRL stars,
our goal in this work is to search for these in association to intermediate-age
clusters whose reliable ages can then be safely be attributed to the RRL. We
used the Gaia DR3 Specific Object Study and OGLE IV public catalogues to search
for RRL stars around stellar clusters older than 1~Gyr in the Large and Small
Magellanic Clouds. Modelling membership probabilities based on proper motion
and photometric distance we obtained a list of 302 RRL stars associated with
Magellanic clusters. Of these, 23 RRL are likely members of 10 intermediate-age
clusters: 3 and 7 in the Small and Large Magellanic Clouds, respectively. By
modelling the inferred expectation values of the number of RRL stars per
cluster, we inferred the delay time distribution of the RRL in three age
ranges. For the old population ($>8$~Gyr) we find $2.6^{+0.4}_{-0.3}$ RRL$/10^5
M_\odot$. For the young (1-2 Gyr) and intermediate age (2-8 Gyr) populations we
find rates of $0.9^{+0.3}_{-0.2}$ and $0.27^{+0.1}_{-0.09}$ RRL$/10^5 M_\odot$,
respectively. While radial velocities are necessary for definitively confirming
cluster memberships, the high-probability list of intermediate-age RRL stars
presented here offers a promising opportunity for the first direct confirmation
of these enigmatic stars.
15 Nov24
Title: Distribution of Europium in The Milky Way Disk
Its Connection to Planetary Habitability and The Source of The R-Process
Authors: Evan M. Carrasco, Matthew Shetrone, Francis Nimmo, Enrico
Ramirez-Ruiz, Joel Primack, Natalie M. Batalha
PDF:https://arxiv.org/pdf/2411.10711
.pdf
Title: The Black Hole$-$Stellar Mass Relation in the Dwarf-galaxy Regime with
$Gaia$-Sausage/Enceladus and $\omega$Centauri
Authors: Guilherme Limberg
https://arxiv.org/pdf/2411.11251
.pdf
Abstract:
The discovery of fast moving stars in the Milky Way's most massive globular
cluster, $\omega$Centauri ($\omega$Cen), has provided strong evidence for an
intermediate-mass black hole (IMBH) inside of it. However, $\omega$Cen is known
to be the stripped nuclear star cluster (NSC) of an ancient, now-destroyed,
dwarf galaxy. The best candidate to be the original host progenitor of
$\omega$Cen is the tidally disrupted dwarf $Gaia$-Sausage/Enceladus (GSE), a
former Milky Way satellite as massive as the Large Magellanic Cloud. I compare
$\omega$Cen/GSE with other central BH hosts and place it within the broader
context of BH-galaxy (co)evolution. The IMBH of $\omega$Cen/GSE follows the
scaling relation between central BH mass and host stellar mass (${\rm M}_{\rm
BH}{-}{\rm M}_\star$) extrapolated from local massive galaxies (${\rm M}_\star
\gtrsim 10^{10}\,{\rm M}_\odot$). Therefore, the IMBH of $\omega$Cen/GSE
suggests that this relation extends to the dwarf-galaxy regime. I verify that
$\omega$Cen (GSE), as well as other NSCs with candidate IMBHs and ultracompact
dwarf galaxies, also follow the ${\rm M}_{\rm BH}{-}\sigma_\star$ relation with
stellar velocity dispersion. Under the assumption of a direct collapse BH,
$\omega$Cen/GSE's IMBH would require a low initial mass ($\lesssim$10,000 ${\rm
M}_{\odot}$) and almost no accretion over $\sim$3 Gyr, which could be the
extreme opposite of high-$z$ galaxies with overmassive BHs such as GN-z11. If
$\omega$Cen/GSE's IMBH formed from a Population III supernova remnant, then it
could indicate that both light and heavy seeding mechanisms of central BH
formation are at play. Other stripped NSCs and dwarf galaxies could help
further populate the ${\rm M}_{\rm BH}{-}{\rm M}_{\star}$ and ${\rm M}_{\rm
BH}{-}\sigma_\star$ relations in the low-mass regime and constraint IMBH
demographics and their formation channels.
Title: Lack of Bulge Alignment in Late-type Galaxies with Large-scale Filaments
Suggests a Radial Migration Formation Scenario
Authors: Wenxiao Xue, Yu Rong
https://arxiv.org/pdf/2411.11438
.pdf
Abstract:
The formation sequence of bulges and disks in late-type galaxies (LTGs)
remains a subject of debate. Some studies propose that the bulge is present
early in galaxy formation, with the disk forming later, while others suggest
the disk forms first, followed by bulge development. This ongoing discussion
highlights the necessity for additional observational and simulation-based
investigations to enhance our understanding. In this study, utilizing a
bulge+disk decomposition catalog for a large LTG sample, we examine, for the
first time, the alignment between the major axes of central bulge components
and their host large-scale filaments. Our analysis indicates no significant
alignment signal for the bulge components. However, we observe alignment
between the major axes of central bulges and outer disks in the sky plane,
suggesting that the formation of central bulges in LTGs may be influenced by,
or even driven by, the migration of components from the outer disks. Our
results offer a novel perspective on bulge formation mechanisms from an
alignment standpoint, providing unique insights for related research endeavors.
Title: Formation of Compact Hierarchical Triples
Authors: Ayush Moharana, K.G. Helminiak, T. Pawar, and G. Pawar
https://arxiv.org/pdf/2411.11459
.pdf
Abstract:
Compact hierarchical triples (CHTs) are triple stars where the tertiary is in
an orbit of a period less than 1000 d. They were thought to be rare but we are
discovering more of these systems recently, thanks to space-based missions like
TESS, Kepler, and GAIA. In this work, we use orbital parameters obtained from
these missions to constrain the formation process of CHTs. We also use
spectroscopic and systemic parameters from our work, and the literature to
understand the effects of metallicity and dynamics on the formation processes.
Title: Bridge the Cosmological Tensions with Thawing Gravity
Authors: Gen Ye
https://arxiv.org/pdf/2411.11743
.pdf
Abstract:
It is found that a non-minimally coupled scalar tensor theory, Thawing
Gravity (TG), can explain multiple tensions plaguing the standard cosmological
model $\Lambda$CDM while fitting better to observations than the latter. Using
the standard Bayes model comparison method, TG has moderate evidence over
$\Lambda$CDM with a Bayes factor $\ln B=+1.5$ in the baseline analysis
including CMB, BAO and SNIa. In the baseline+$H_0$ analysis which further takes
into account the Cepheids calibration of the SNIa distance ladder from SH0ES,
TG has very strong evidence over $\Lambda$CDM with $\ln B=+11.8$. In
particular, TG yields $H_0=71.78\pm0.86 \ {\rm km/s/Mpc}$ and
$S_8=0.793\pm0.012$, consistent with both local $H_0$ measurement and the large
scale structure surveys.
14 Nov24
Title: The Exoplanet Edge: Planets Don't Induce Observable TTVs Faster than Half their Orbital Period
Authors: Daniel A. Yahalomi, David Kipping, Eric Agol, and David Nesvorny
https://arxiv.org/pdf/2411.09752
.pdf
Abstract:
Transit timing variations (TTVs) are observed for exoplanets at a range of
amplitudes and periods, yielding an ostensibly degenerate forest of possible
explanations. We offer some clarity in this forest, showing that systems with a
distant perturbing planet preferentially show TTVs with a dominant period equal
to either the perturbing planet's period or half the perturbing planet's
period. We demonstrate that planet induced TTVs are not expected with TTV
periods below this exoplanet edge (lower period limit) and that systems with
TTVs that fall below this limit likely contain additional mass in the system.
We present an explanation for both of these periods, showing that both aliasing
of the conjunction induced synodic period and the near $1:2$ resonance
super-period and tidal effects induce TTVs at periods equal to either the
perturber's orbit or half-orbit. We provide three examples of known systems for
which the recovered TTV period induced by a distant perturbing planet is equal
to the perturber's orbital period or half its orbital period. We then
investigate $\textit{Kepler}$ two-planet systems with TTVs and identify 13
two-planet systems with TTVs below this TTV period lower limit -- thus
potentially uncovering the gravitational influence of new planets and/or moons.
We conclude by discussing how the exoplanet edge effects can be used to predict
the presence of distance companion planets, in situations where TTVs are
detected and where nearby companions can be ruled out by additional
observations, such as radial velocity data.
Title: Self-Excited Pulsations and the Instability Strip of Long-Period
Variables: the Transition from Small-Amplitude Red Giants to Semi-Regular
Variables
Authors: Michele Trabucchi and Giada Pastorelli
https://arxiv.org/pdf/2411.10341
.pdf
Abstract:
We use one-dimensional hydrodynamic calculations combined with synthetic
stellar population models of the Magellanic Clouds to study the onset of
self-excited pulsation in luminous red giants. By comparing the results with
OGLE observations in the period-luminosity diagram we are able to link the
transition from small-amplitude red giants to semi-regular variables with a
shift from stochastic driving to self-excited pulsations. This is consistent
with previous studies relating this transition with an increase in mass-loss
rate, dust formation, and the appearance of long secondary periods. The
luminosity and effective temperature at the onset of pulsation are found to
depend on metallicity, hydrogen content, and the adopted mixing length
parameter. This confirms the role of partial hydrogen ionization in driving the
pulsation, supporting the idea of a heat mechanism similar to that of classical
pulsators. We examine the impact of turbulent viscosity, and find clear
evidence that it must be adjusted according to the stellar chemical and
physical parameters to fully match observations. In order to improve the
predictive power of pulsation models, the turbulent viscosity and the
temperature scale of pulsating red giants must be jointly calibrated. This is
critical for model-based studies of the period-luminosity relations of evolved
stars and to exploit their potential as distance and age indicators, in
particular given the sensitivity of the onset of pulsation to the envelope
composition. The grid of models is made publicly available with a companion
interpolation routine.