5 research outputs found
SGAS 143845.1+145407: A Big, Cool Starburst at Redshift 0.816
We present the discovery and a detailed multi-wavelength study of a
strongly-lensed luminous infrared galaxy at z=0.816. Unlike most known lensed
galaxies discovered at optical or near-infrared wavelengths this lensed source
is red, r-Ks = 3.9 [AB], which the data presented here demonstrate is due to
ongoing dusty star formation. The overall lensing magnification (a factor of
17) facilitates observations from the blue optical through to 500micron, fully
capturing both the stellar photospheric emission as well as the re-processed
thermal dust emission. We also present optical and near-IR spectroscopy. These
extensive data show that this lensed galaxy is in many ways typical of
IR-detected sources at z~1, with both a total luminosity and size in accordance
with other (albeit much less detailed) measurements in samples of galaxies
observed in deep fields with the Spitzer telescope. Its far-infrared spectral
energy distribution is well-fit by local templates that are an order of
magnitude less luminous than the lensed galaxy; local templates of comparable
luminosity are too hot to fit. Its size (D~7kpc) is much larger than local
luminous infrared galaxies, but in line with sizes observed for such galaxies
at z~1. The star formation appears uniform across this spatial scale. In this
source, the luminosity of which is typical of sources that dominate the cosmic
infrared background, we find that star formation is spatially extended and well
organised, quite unlike the compact merger-driven starbursts which are typical
for sources of this luminosity at z~0.Comment: 18 pages, 10 figure
An Empirical Characterization of Extended Cool Gas Around Galaxies Using MgII Absorption Features
We report results from a survey of MgII absorbers in the spectra of
background QSOs that are within close angular distances to a foreground galaxy
at z<0.5, using the Magellan Echellette Spectrograph. We have established a
spectroscopic sample of 94 galaxies at a median redshift of = 0.24 in
fields around 70 distant background QSOs (z_QSO>0.6), 71 of which are in an
'isolated' environment with no known companions and located at rho <~ 120 h^-1
kpc from the line of sight of a background QSO. The rest-frame absolute B-band
magnitudes span a range from M_B-5log h=-16.4 to M_B-5log h=-21.4 and
rest-frame B_AB-R_AB colors range from B_AB-R_AB~0 to B_AB-R_AB~1.5. Of these
'isolated' galaxies, we find that 47 have corresponding MgII absorbers in the
spectra of background QSOs and rest-frame absorption equivalent width
W_r(2796)=0.1-2.34 A, and 24 do not give rise to MgII absorption to sensitive
upper limits. Our analysis shows that (1) Wr(2796) declines with increasing
distance from 'isolated' galaxies but shows no clear trend in 'group'
environments; (2) more luminous galaxies possess more extended MgII absorbing
halos with the gaseous radius scaled by B-band luminosity according to
R_gas=75x(L_B/L_B*)^(0.35+/-0.03) h^{-1} kpc; (3) there is little dependence
between the observed absorber strength and galaxy intrinsic colors; and (4)
within R_gas, we find a mean covering fraction of ~70% for absorbers
of Wr(2796)>=0.3 A and ~80% for absorbers of Wr(2796)>=0.1 A. The
lack of correlation between Wr(2796) and galaxy colors suggests a lack of
physical connection between the origin of extended MgII halos and recent star
formation history of the galaxies. Finally, we discuss the total gas mass in
galactic halos as traced by MgII absorbers. We also compare our results with
previous studies.Comment: 20 pages, 13 figures; to appear in the Astrophysical Journal 2010 May
10 issue; a version with higher resolution figures can be found at
http://lambda.uchicago.edu/public/tmp/mage_apj.pd