41 research outputs found
Galaxy Evolution from Emission Linewidths
The major thrust of the Tully-Fisher (TF) surveys of distant galaxies is the
measurement of linewidths rather than mere redshifts or colors. Linewidths are
a measure of galaxy mass and should therefore be a more stable indicator of
size than galaxy brightness, which can be badly affected by luminosity
evolution. Masses may provide the best way to relate galaxies at different
epochs, but for such a program to work, we must control systematic effects that
could bias linewidth measurements at high redshift and skew comparisons with
local Tully-Fisher calibrations. Potential sources of confusion in TF studies
of galaxy structure and evolution include central or extended star bursts,
infalling gas, turbulence and outflows, dust extinction, calibration of
emission linewidths, and improper application of local TF calibrations to high
redshift galaxies.Comment: 7 pages, 3 figures; Proceedings contribution in The Mass of Galaxies
at Low and High Redshift, eds. R. Bender and A. Renzini (ESO Astrophysics
Symposia
On the Uncertainties of Stellar Mass Estimates via Colour Measurements
Mass-to-light versus colour relations (MLCRs), derived from stellar
population synthesis models, are widely used to estimate galaxy stellar masses
(M) yet a detailed investigation of their inherent biases and limitations
is still lacking. We quantify several potential sources of uncertainty, using
optical and near-infrared (NIR) photometry for a representative sample of
nearby galaxies from the Virgo cluster. Our method for combining multi-band
photometry with MLCRs yields robust stellar masses, while errors in M
decrease as more bands are simultaneously considered. The prior assumptions in
one's stellar population modelling dominate the error budget, creating a
colour-dependent bias of up to 0.6 dex if NIR fluxes are used (0.3 dex
otherwise). This matches the systematic errors associated with the method of
spectral energy distribution (SED) fitting, indicating that MLCRs do not suffer
from much additional bias. Moreover, MLCRs and SED fitting yield similar
degrees of random error (0.1-0.14 dex) when applied to mock galaxies and,
on average, equivalent masses for real galaxies with M 10
M. The use of integrated photometry introduces additional uncertainty
in M measurements, at the level of 0.05-0.07 dex. We argue that using
MLCRs, instead of time-consuming SED fits, is justified in cases with complex
model parameter spaces (involving, for instance, multi-parameter star formation
histories) and/or for large datasets. Spatially-resolved methods for measuring
M should be applied for small sample sizes and/or when accuracies less than
0.1 dex are required. An Appendix provides our MLCR transformations for ten
colour permutations of the filter set.Comment: Accepted to MNRAS. 43 pages, 12 figures, 3 table
Stripping of the Hot Gas Halos in Member Galaxies of Abell 1795
The nearby cluster Abell 1795 is used as a testbed to examine whether hot gas
in cluster galaxies is stripped by the ram pressure of the intracluster medium
(ICM). The expected X-ray emission in and around Abell 1795 galaxies is likely
dominated by the ICM, low-mass X-ray binaries, active galactic nuclei, and hot
gas halos. In order to constrain these components, we use archival Chandra
X-ray Observatory and Sloan Digital Sky Survey (SDSS) observations of Abell
1795 and identify 58 massive (M_star>10^10 M_sun) spectroscopic cluster members
within 5 arcmin of the Chandra optical axis. X-ray images at 0.5-1.5 keV and
4-8 keV were created for each cluster member and then stacked into two
clustercentric radius bins: inner (0.25<R/R_500<1) and outer (1<R/R_500<2.5).
Surface brightness profiles of inner and outer cluster members are fit using
Markov chain Monte Carlo sampling in order to generate model parameters and
measure the 0.5-1.5 keV luminosities of each model component. Leveraging
effective total Chandra exposure times of 3.4 and 1.7 Msec for inner and outer
cluster members, respectively, we report the detection of hot gas halos, in a
statistical sense, around outer cluster members. Outer members have 0.5-1.5 keV
hot halo luminosities (L_X = 8.1(-3.5/+5)x10^39 erg/s) that are six times
larger than the upper limit for inner cluster members (L_X < 1.3x10^39 erg/s).
This result suggests that the ICM is removing hot gas from the halos of Abell
1795 members as they fall into the cluster.Comment: 15 pages, nine figures, accepted for publication in The Astrophysical
Journa
Stellar Populations in Spiral Galaxies
We report preliminary results of the characterization of bulge and inner disk
stellar populations for 8 nearby spiral galaxies using Gemini/GMOS. The
long-slit spectra extend out to 1-2 disk scale lengths with S/N/Ang > 50. Two
different model fitting techniques, absorption-line indices and full spectral
synthesis, are found to weigh age, metallicity, and abundance ratios
differently, but with careful attention to the data/model matching (resolution
and flux calibration), we are able constrain real signatures of age and
metallicity gradients in star-forming galaxies.Comment: 4 pages, 3 figures. To appear in the proceedings for IAUS 241
"Stellar Populations as Building Blocks of Galaxies", Eds. R.F. Peletier and
A. Vazdeki