123 research outputs found
RETROCAM: A Versatile Optical Imager for Synoptic Studies
We present RETROCAM, an auxiliary CCD camera that can be rapidly inserted
into the optical beam of the MDM 2.4m telescope. The speed and ease of
reconfiguring the telescope to use the imager and a straightforward user
interface permit the camera to be used during the course of other observing
programs. This in turn encourages RETROCAM's use for a variety of monitoring
projects.Comment: 6 pages, 6 figures, Accepted by A
ASASSN-16ae: A Powerful White-Light Flare on an Early-L Dwarf
We report the discovery and classification of SDSS~J053341.43+001434.1
(SDSS0533), an early-L dwarf first discovered during a powerful magnitude flare observed as part of the ASAS-SN survey. Optical and
infrared spectroscopy indicate a spectral type of L0 with strong H
emission and a blue NIR spectral slope. Combining the photometric distance,
proper motion, and radial velocity of SDSS0533 yields three-dimensional
velocities of ~km~s, indicating
that it is most likely part of the thick disk population and probably old. The
three detections of SDSS0533 obtained during the flare are consistent with a
total -band flare energy of at least ~ergs (corresponding
to a total thermal energy of at least ~erg),
placing it among the strongest detected M dwarf flares. The presence of this
powerful flare on an old L0 dwarf may indicate that stellar-type magnetic
activity persists down to the end of the main sequence and on older ML
transition dwarfs.Comment: 7 pages, 3 tables, 2 figures; accepted to ApJ Letters; updated to
reflect referee response and proof correction
The Clustering of Extremely Red Objects
We measure the clustering of Extremely Red Objects (EROs) in ~8 deg^2 of the
NOAO Deep Wide Field Survey Bo\"otes field in order to establish robust links
between ERO z~1.2 and local galaxy z<0.1 populations. Three different color
selection criteria from the literature are analyzed to assess the consequences
of using different criteria for selecting EROs. Specifically, our samples are
(R-K_s)>5.0 (28,724 galaxies), (I-K_s)>4.0 (22,451 galaxies) and (I-[3.6])>5.0
(64,370 galaxies). Magnitude-limited samples show the correlation length (r_0)
to increase for more luminous EROs, implying a correlation with stellar mass.
We can separate star-forming and passive ERO populations using the (K_s-[24])
and ([3.6]-[24]) colors to K_s=18.4 and [3.6]=17.5, respectively. Star-forming
and passive EROs in magnitude limited samples have different clustering
properties and host dark halo masses, and cannot be simply understood as a
single population. Based on the clustering, we find that bright passive EROs
are the likely progenitors of >4L^* elliptical galaxies. Bright EROs with
ongoing star formation were found to occupy denser environments than
star-forming galaxies in the local Universe, making these the likely
progenitors of >L^* local ellipticals. This suggests that the progenitors of
massive >4L^* local ellipticals had stopped forming stars by z>1.2, but that
the progenitors of less massive ellipticals (down to L^*) can still show
significant star formation at this epoch.Comment: 19 pages, 16 figures, 4 tables, Accepted to ApJ 27th November 201
Adaptive Optics Imaging of a Massive Galaxy Associated with a Metal-rich Absorber
The damped and sub-damped Lyman-alpha absorption line systems in quasar
spectra are believed to be produced by intervening galaxies. However, the
connection of quasar absorbers to galaxies is not well-understood, since
attempts to image the absorbing galaxies have often failed. While most DLAs
appear to be metal-poor, a population of metal-rich absorbers, mostly sub-DLAs,
has been discovered in recent studies. Here we report high-resolution K-band
imaging with the Keck Laser Guide Star Adaptive Optics (LGSAO) system of the
field of quasar SDSSJ1323-0021 in search of the galaxy producing the z = 0.72
sub-DLA absorber. With a metallicity of 2-4 times the solar level, this
absorber is of the most metal-rich systems found to date. Our data show a large
bright galaxy with an angular separation of only 1.25" from the quasar,
well-resolved from the quasar at the high resolution of our data. The galaxy
has a magnitude of K = 17.6-17.9, which corresponds to a luminosity of ~ 3-6
L*. Morphologically, the galaxy is fit with a model with an effective radius,
enclosing half the total light, of R_e = 4 kpc and a bulge-to-total ratio of
0.4-1.0, indicating a substantial bulge stellar population. Based on the
mass-metallicity relation of nearby galaxies, the absorber galaxy appears to
have a stellar mass > 10^{11} M_sun. Given the small impact parameter, this
massive galaxy appears to be responsible for the metal-rich sub-DLA. The
absorber galaxy is consistent with the metallicity-luminosity relation observed
for nearby galaxies, but is near the upper end of metallicity. Our study marks
the first application of LGSAO for study of structure of galaxies producing
distant quasar absorbers. Finally, this study offers the first example of a
massive galaxy with a substantial bulge producing a metal-rich absorber.Comment: 17 pages, 4 figures, 1 table; Accepted for publication in The
Astronomical Journa
The Formation of Massive Cluster Galaxies
We present composite 3.6 and 4.5 micron luminosity functions for cluster
galaxies measured from the Spitzer Deep, Wide-Field Survey (SDWFS) for 0.3<z<2.
We compare the evolution of m* for these luminosity functions to models for
passively evolving stellar populations to constrain the primary epoch of star
formation in massive cluster galaxies. At low redshifts (z < 1.3) our results
agree well with models with no mass assembly and passively evolving stellar
populations with a luminosity-weighted mean formation redshift zf=2.4 assuming
a Kroupa initial mass function (IMF). We conduct a thorough investigation of
systematic biases that might influence our results, and estimate systematic
uncertainites of Delta zf=(+0.16-0.18) (model normalization), Delta
zf=(+0.40-0.05) (alpha), and Delta zf=(+0.30-0.45) (choice of stellar
population model). For a Salpeter type IMF, the typical formation epoch is thus
strongly constrained to be z ~2-3. Higher formation redshifts can only be made
consistent with the data if one permits an evolving IMF that is bottom-light at
high redshift, as suggested by van Dokkum et al 2008. At high redshift (z >
1.3) we also witness a statistically significant (>5sigma) disagreement between
the measured luminosity function and the continuation of the passive evolution
model from lower redshifts. After considering potential systematic biases that
might influence our highest redshift data points, we interpret the observed
deviation as potential evidence for ongoing mass assembly at this epoch.Comment: 17 pages, 14 figures, accepted for publication in Ap
The Clustering and Halo Masses of Star Forming Galaxies at z<1
We present clustering measurements and halo masses of star forming galaxies
at 0.2 < z < 1.0. After excluding AGN, we construct a sample of 22553 24 {\mu}m
sources selected from 8.42 deg^2 of the Spitzer MIPS AGN and Galaxy Evolution
Survey of Bo\"otes. Mid-infrared imaging allows us to observe galaxies with the
highest star formation rates (SFRs), less biased by dust obscuration afflicting
the optical bands. We find that the galaxies with the highest SFRs have optical
colors which are redder than typical blue cloud galaxies, with many residing
within the green valley. At z > 0.4 our sample is dominated by luminous
infrared galaxies (LIRGs, L_TIR > 10^11 Lsun) and is comprised entirely of
LIRGs and ultra-luminous infrared galaxies (ULIRGs, L_TIR > 10^12 Lsun) at z >
0.6. We observe weak clustering of r_0 = 3-6 Mpc/h for almost all of our star
forming samples. We find that the clustering and halo mass depend on L_TIR at
all redshifts, where galaxies with higher L_TIR (hence higher SFRs) have
stronger clustering. Galaxies with the highest SFRs at each redshift typically
reside within dark matter halos of M_halo ~ 10^12.9 Msun/h. This is consistent
with a transitional halo mass, above which star formation is largely truncated,
although we cannot exclude that ULIRGs reside within higher mass halos. By
modeling the clustering evolution of halos, we connect our star forming galaxy
samples to their local descendants. Most star forming galaxies at z < 1.0 are
the progenitors of L < 2.5L* blue galaxies in the local universe, but star
forming galaxies with the highest SFRs (L_TIR >10^11.7 Lsun) at 0.6<z<1.0 are
the progenitors of early-type galaxies in denser group environments.Comment: 18 pages, 16 figures, 2 tables. Accepted for publication in the
Astrophysical Journa
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