6 research outputs found
The Intrinsic Shapes of Low Surface Brightness Galaxies (LSBGs):A Discriminant of LSBG Galaxy Formation Mechanisms
We use the low surface brightness galaxy (LSBG) samples created from the Hyper Suprime-Cam Subaru Strategic Program (781 galaxies), the Dark Energy Survey (20977 galaxies), and the Legacy Survey (selected via H I detection in the Arecibo Legacy Fast ALFA Survey, 188 galaxies) to infer the intrinsic shape distribution of the LSBG population. To take into account the effect of the surface brightness cuts employed when constructing LSBG samples, we simultaneously model both the projected ellipticity and the apparent surface brightness in our shape inference. We find that the LSBG samples are well characterized by oblate spheroids, with no significant difference between red and blue LSBGs. This inferred shape distribution is in good agreement with similar inferences made for ultra-diffuse cluster galaxy samples, indicating that environment does not play a key role in determining the intrinsic shape of LSBGs. We also find some evidence that LSBGs are more thickened than similarly massive high surface brightness dwarfs. We compare our results to intrinsic shape measures from contemporary cosmological simulations, and find that the observed LSBG intrinsic shapes place considerable constraints on the formation path of such galaxies. In particular, LSBG production via the migration of star formation to large radii produces intrinsic shapes in good agreement with our observational findings
The Very Short Period M Dwarf Binary SDSS J001641-000925
We present follow-up observations and analysis of the recently discovered
short period low-mass eclipsing binary, SDSS J001641-000925. With an orbital
period of 0.19856 days, this system has one of the shortest known periods for
an M dwarf binary system. Medium-resolution spectroscopy and multi-band
photometry for the system are presented. Markov chain Monte Carlo modeling of
the light curves and radial velocities yields estimated masses for the stars of
M1 = 0.54 +/- 0.07 Msun and M2 = 0.34 +/- 0.04 Msun, and radii of R1 = 0.68 +/-
0.03 Rsun and R2 = 0.58 +/- 0.03 Rsun respectively. This solution places both
components above the critical Roche overfill limit, providing strong evidence
that SDSS J001641-000925 is the first verified M-dwarf contact binary system.
Within the follow-up spectroscopy we find signatures of non-solid body rotation
velocities, which we interpret as evidence for mass transfer or loss within the
system. In addition, our photometry samples the system over 9 years, and we
find strong evidence for period decay at the rate of dP/dt ~8 s/yr. Both of
these signatures raise the intriguing possibility that the system is in
over-contact, and actively losing angular momentum, likely through mass loss.
This places SDSS J001641-000925 as not just the first M-dwarf over-contact
binary, but one of the few systems of any spectral type known to be actively
undergoing coalescence. Further study SDSS J001641-000925 is on-going to verify
the nature of the system, which may prove to be a unique astrophysical
laboratory.Comment: 11 figures, ApJ Accepte
Reproducing the Stellar Mass/Halo Mass Relation in Simulated LCDM Galaxies: Theory vs Observational Estimates
We examine the present-day total stellar-to-halo mass (SHM) ratio as a
function of halo mass for a new sample of simulated field galaxies using fully
cosmological, LCDM, high resolution SPH + N-Body simulations.These simulations
include an explicit treatment of metal line cooling, dust and self-shielding,
H2 based star formation and supernova driven gas outflows. The 18 simulated
halos have masses ranging from a few times 10^8 to nearly 10^12 solar masses.
At z=0 our simulated galaxies have a baryon content and morphology typical of
field galaxies. Over a stellar mass range of 2.2 x 10^3 to 4.5 x 10^10 solar
masses, we find extremely good agreement between the SHM ratio in simulations
and the present-day predictions from the statistical Abundance Matching
Technique presented in Moster et al. (2012). This improvement over past
simulations is due to a number systematic factors, each decreasing the SHM
ratios: 1) gas outflows that reduce the overall SF efficiency but allow for the
formation of a cold gas component 2) estimating the stellar masses of simulated
galaxies using artificial observations and photometric techniques similar to
those used in observations and 3) accounting for a systematic, up to 30 percent
overestimate in total halo masses in DM-only simulations, due to the neglect of
baryon loss over cosmic times. Our analysis suggests that stellar mass
estimates based on photometric magnitudes can underestimate the contribution of
old stellar populations to the total stellar mass, leading to stellar mass
errors of up to 50 percent for individual galaxies. These results highlight the
importance of using proper techniques to compare simulations with observations
and reduce the perceived tension between the star formation efficiency in
galaxy formation models and in real galaxies.Comment: Submitted to ApJ 9 pages, 5 figure
Report of the Topical Group on Cosmic Probes of Dark Matter for Snowmass 2021
Cosmological and astrophysical observations currently provide the only
robust, positive evidence for dark matter. Cosmic probes of dark matter, which
seek to determine the fundamental properties of dark matter through
observations of the cosmos, have emerged as a promising means to reveal the
nature of dark matter. This report summarizes the current status and future
potential of cosmic probes to inform our understanding of the fundamental
nature of dark matter in the coming decade.Comment: Report of the CF3 Topical Group for Snowmass 2021; 35 pages, 10
figures, many references. V3 updates Fig 3-2 and the author lis