174 research outputs found
The Large-scale Distribution of Cool Gas around Luminous Red Galaxies
We present a measurement of the correlation function between luminous red
galaxies and cool gas traced by Mg II \lambda \lambda 2796, 2803 absorption, on
scales ranging from about 30 kpc to 20 Mpc. The measurement is based on
cross-correlating the positions of about one million red galaxies at z~0.5 and
the flux decrements induced in the spectra of about 10^5 background quasars
from the Sloan Digital Sky Survey. We find that: (i) This galaxy-gas
correlation reveals a change of slope on scales of about 1 Mpc, consistent with
the expected transition from a dark matter halo dominated environment to a
regime where clustering is dominated by halo-halo correlations. Assuming that,
on average, the distribution of Mg II gas follows that of dark matter up to a
gas-to-mass ratio, we find the standard halo model to provide an accurate
description of the gas distribution over three orders of magnitude in scale.
Within this framework we estimate the average host halo mass of luminous red
galaxies to be about 10^{13.5} M_solar, in agreement with other methods. We
also find the Mg II gas-to-mass ratio around LRGs to be consistent with the
cosmic value estimated on Mpc scales. Combining our galaxy-gas correlation and
the galaxy-mass correlation function from galaxy-galaxy lensing analyses we can
directly measure the Mg II gas-to-mass ratio as a function of scale and reach
the same conclusion. (ii) From line-width estimates, we show that the velocity
dispersion of the gas clouds also shows the expected 1- and 2-halo behaviors.
On large scales the gas distribution follows the Hubble flow, whereas on small
scales we observe the velocity dispersion of the Mg II gas clouds to be lower
than that of collisionless dark matter particles within their host halo. This
is in line with the fact that cool clouds are subject to the pressure of the
virialized hot gas.Comment: 18 pages, 11 figures, 1 table, submitted to MNRA
APOGEE Kinematics I: Overview of the Kinematics of the Galactic Bulge as Mapped by APOGEE
We present the stellar kinematics across the Galactic bulge and into the disk
at positive longitudes from the SDSS-III APOGEE spectroscopic survey of the
Milky Way. APOGEE includes extensive coverage of the stellar populations of the
bulge along the mid-plane and near-plane regions. From these data, we have
produced kinematic maps of 10,000 stars across longitudes 0 deg < l < 65 deg,
and primarily across latitudes of |b| < 5 deg in the bulge region. The APOGEE
data reveal that the bulge is cylindrically rotating across all latitudes and
is kinematically hottest at the very centre of the bulge, with the smallest
gradients in both kinematic and chemical space inside the inner-most region
(l,|b|) < (5,5) deg. The results from APOGEE show good agreement with data from
other surveys at higher latitudes and a remarkable similarity to the rotation
and dispersion maps of barred galaxies viewed edge on. The thin bar that is
reported to be present in the inner disk within a narrow latitude range of |b|
< 2 deg appears to have a corresponding signature in [Fe/H] and [alpha/Fe].
Stars with [Fe/H] > -0.5 have dispersion and rotation profiles that are similar
to that of N-body models of boxy/peanut bulges. There is a smooth kinematic
transition from the thin bar and boxy bulge (l,|b|) < (15,12) deg out into the
disk for stars with [Fe/H] > -1.0, and the chemodynamics across (l,b) suggests
the stars in the inner Galaxy with [Fe/H] > -1.0 have an origin in the disk.Comment: Accepted by ApJ 15 December 201
The Sloan Digital Sky Survey Reverberation Mapping Project: Ensemble Spectroscopic Variability of Quasar Broad Emission Lines
We explore the variability of quasars in the MgII and Hbeta broad emission
lines and UV/optical continuum emission using the Sloan Digital Sky Survey
Reverberation Mapping project (SDSS-RM). This is the largest spectroscopic
study of quasar variability to date: our study includes 29 spectroscopic epochs
from SDSS-RM over months, containing 357 quasars with MgII and 41 quasars
with Hbeta . On longer timescales, the study is also supplemented with
two-epoch data from SDSS-I/II. The SDSS-I/II data include an additional
quasars with MgII and 572 quasars with Hbeta. The MgII emission line is
significantly variable ( 10% on 100-day timescales), a necessary
prerequisite for its use for reverberation mapping studies. The data also
confirm that continuum variability increases with timescale and decreases with
luminosity, and the continuum light curves are consistent with a damped
random-walk model on rest-frame timescales of days. We compare the
emission-line and continuum variability to investigate the structure of the
broad-line region. Broad-line variability shows a shallower increase with
timescale compared to the continuum emission, demonstrating that the broad-line
transfer function is not a -function. Hbeta is more variable than MgII
(roughly by a factor of ), suggesting different excitation mechanisms,
optical depths and/or geometrical configuration for each emission line. The
ensemble spectroscopic variability measurements enabled by the SDSS-RM project
have important consequences for future studies of reverberation mapping and
black hole mass estimation of quasars.Comment: 20 pages, 25 figures. ApJ accepted: minor revisions following referee
repor
Close companions around young stars
Multiplicity is a fundamental property that is set early during stellar
lifetimes, and it is a stringent probe of the physics of star formation. The
distribution of close companions around young stars is still poorly constrained
by observations. We present an analysis of stellar multiplicity derived from
APOGEE-2 spectra obtained in targeted observations of nearby star-forming
regions. This is the largest homogeneously observed sample of high-resolution
spectra of young stars. We developed an autonomous method to identify double
lined spectroscopic binaries (SB2s). Out of 5007 sources spanning the mass
range of 0.05--1.5 \msun, we find 399 binaries, including both RV
variables and SB2s. The mass ratio distribution of SB2s is consistent with a
uniform for . The period
distribution is consistent with what has been observed in close binaries (
AU) in the evolved populations. Three systems are found to have 0.1,
with a companion located within the brown dwarf desert. There are not any
strong trends in the multiplicity fraction (MF) as a function of cluster age
from 1 to 100 Myr. There is a weak dependence on stellar density, with
companions being most numerous at stars/pc, and
decreasing in more diffuse regions. Finally, disk-bearing sources are deficient
in SB2s (but not RV variables) by a factor of 2; this deficit is
recovered by the systems without disks. This may indicate a quick dispersal of
disk material in short-period equal mass systems that is less effective in
binaries with lower .Comment: 25 pages, 20 figures. Accepted to A
Evolution of Star-forming Galaxies from z=0.7 to 1.2 with eBOSS Emission-line Galaxies
We study the evolution of star-forming galaxies with 10 10 M ⊙ < M ∗ < 10 11.6 M ⊙ over the redshift range of 0.7 < z < 1.2 using the emission-line galaxies (ELGs) in the extended Baryon Oscillation Spectroscopic Survey (eBOSS). By applying the incomplete conditional stellar mass function (SMF) model proposed in Guo et al., we simultaneously constrain the sample completeness, the stellariVhalo mass relation (SHMR), and the quenched galaxy fraction. We obtain the intrinsic SMFs for star-forming galaxies in the redshift bins of 0.7 < z < 0.8, 0.8 < z < 0.9, 0.9 < z < 1.0, and 1.0 < z < 1.2, as well as the SMF for all galaxies in the redshift bin of 0.7 < z < 0.8. We find that the eBOSS ELG sample only selects about 1%-10% of the star-forming galaxy population at the different redshifts, with the lower redshift samples more complete. There is only weak evolution in the SHMR of the ELGs from z = 1.2 to z = 0.7, as well as the intrinsic galaxy SMFs. Our best-fitting models show that the central ELGs at these redshifts live in halos of mass M ∼ 10 12 M ⊙ , while the satellite ELGs occupy slightly more massive halos of M ∼ 10 12.6 M ⊙ . The average satellite fraction of the observed ELGs varies from 13% to 17%, with the galaxy bias increasing from 1.1 to 1.4 from z = 0.7 to 1.2
The Sloan Digital Sky Survey Reverberation Mapping Project : systematic investigations of short-timescale CIV broad absorption line variability
We systematically investigate short-timescale (<10-day rest-frame) Civ broad absorption-line (BAL) variability to constrain quasar-wind properties and provide insights into BAL-variability mechanisms in quasars. We employ data taken by the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project, as the rapid cadence of these observations provides a novel opportunity to probe BAL variability on shorter rest-frame timescales than have previously been explored. In a sample of 27 quasars with a median of 58 spectral epochs per quasar, we have identified 15 quasars (55+18−14%), 19 of37 Civ BAL troughs (51+15−12%), and 54 of 1460 epoch pairs (3.7±0.5%) that exhibit significant CivBAL equivalent-width variability on timescales of less than 10 days in the quasar rest frame. These frequencies indicate that such variability is common among quasars and BALs, though somewhat rare among epoch pairs. Thus, models describing BALs and their behavior must account for variability on timescales down to less than a day in the quasar rest frame. We also examine a variety of spectral characteristics and find that in some cases, BAL variability is best described by ionization-state changes, while other cases are more consistent with changes in covering fraction or column density. We adopt a simple model to constrain the density and radial distance of two outflows appearing to vary by ionization-state changes, yielding outflow density lower limits consistent with previous work.PostprintPeer reviewe
High-resolution, H band Spectroscopy of Be Stars with SDSS-III/APOGEE: I. New Be Stars, Line Identifications, and Line Profiles
APOGEE has amassed the largest ever collection of multi-epoch,
high-resolution (R~22,500), H-band spectra for B-type emission line (Be) stars.
The 128/238 APOGEE Be stars for which emission had never previously been
reported serve to increase the total number of known Be stars by ~6%. We focus
on identification of the H-band lines and analysis of the emission peak
velocity separations (v_p) and emission peak intensity ratios (V/R) of the
usually double-peaked H I and non-hydrogen emission lines. H I Br11 emission is
found to preferentially form in the circumstellar disks at an average distance
of ~2.2 stellar radii. Increasing v_p toward the weaker Br12--Br20 lines
suggests these lines are formed interior to Br11. By contrast, the observed IR
Fe II emission lines present evidence of having significantly larger formation
radii; distinctive phase lags between IR Fe II and H I Brackett emission lines
further supports that these species arise from different radii in Be disks.
Several emission lines have been identified for the first time including
~16895, a prominent feature in the spectra for almost a fifth of the sample
and, as inferred from relatively large v_p compared to the Br11-Br20, a tracer
of the inner regions of Be disks. Unlike the typical metallic lines observed
for Be stars in the optical, the H-band metallic lines, such as Fe II 16878,
never exhibit any evidence of shell absorption, even when the H I lines are
clearly shell-dominated. The first known example of a quasi-triple-peaked Br11
line profile is reported for HD 253659, one of several stars exhibiting intra-
and/or extra-species V/R and radial velocity variation within individual
spectra. Br11 profiles are presented for all discussed stars, as are full
APOGEE spectra for a portion of the sample.Comment: accepted in A
P-MaNGA : full spectral fitting and stellar population maps from prototype observations
MC acknowledges support from a Royal Society University Research Fellowship.MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a 6-yearSDSS-IV survey that will obtain resolved spectroscopy from 3600 Å to10300 Å for a representative sample of over 10,000 nearby galaxies.In this paper, we derive spatially resolved stellar population properties and radial gradients by performing full spectral fitting of observed galaxy spectra from P-MaNGA, a prototype of the MaNGA instrument. These data include spectra for eighteen galaxies, covering a large range of morphological type. We derive age, metallicity, dust and stellar mass maps, and their radial gradients, using high spectral-resolution stellar population models, and assess the impact of varying the stellar library input to the models. We introduce a method to determine dust extinction which is able to give smooth stellar mass maps even in cases of high and spatially non-uniform dust attenuation.With the spectral fitting we produce detailed maps of stellar population properties which allow us to identify galactic features among this diverse sample such as spiral structure, smooth radial profiles with little azimuthal structure in spheroidal galaxies, and spatially distinct galaxy sub-components. In agreement with the literature, we find the gradients for galaxies identified as early-type to be on average flat in age, and negative (- 0.15 dex / Re ) in metallicity,whereas the gradients for late-type galaxies are on average negative in age (- 0.39 dex / Re ) and flat in metallicity. We demonstrate howdifferent levels of data quality change the precision with which radialgradients can be measured. We show how this analysis, extended to thelarge numbers of MaNGA galaxies, will have the potential to shed lighton galaxy structure and evolution.PostprintPeer reviewe
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