8 research outputs found
A MegaCam Survey of Outer Halo Satellites. I. Description of the Survey
We describe a deep, systematic imaging study of satellites in the outer halo
of the Milky Way. Our sample consists of 58 stellar overdensities --- i.e.,
substructures classified as either globular clusters, classical dwarf galaxies,
or ultra-faint dwarf galaxies --- that are located at Galactocentric distances
of R > 25 kpc (outer halo) and out to ~400 kpc. This includes 44
objects for which we have acquired deep, wide-field, and band imaging
with the MegaCam mosaic cameras on the 3.6m Canada-France-Hawaii Telescope and
the 6.5m Magellan-Clay telescope. These data are supplemented by archival
imaging, or published photometry, for an additional 14 objects, most of
which were discovered recently in the Dark Energy Survey (DES). We describe the
scientific motivation for our survey, including sample selection, observing
strategy, data reduction pipeline, calibration procedures, and the depth and
precision of the photometry. The typical 5 point-source limiting
magnitudes for our MegaCam imaging --- which collectively covers an area of ~52
deg --- are ~25.6 and ~25.3 AB mag. These
limits are comparable to those from the coadded DES images and are roughly a
half-magnitude deeper than will be reached in a single visit with LSST. Our
photometric catalog thus provides the deepest and most uniform photometric
database of Milky Way satellites available for the foreseeable future. In other
papers in this series, we have used these data to explore the blue straggler
populations in these objects, their density distributions, star formation
histories, scaling relations and possible foreground structures.Comment: Accepted for publication in Ap
A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters
We present structural parameters from a wide-field homogeneous imaging survey
of Milky Way satellites carried out with the MegaCam imagers on the 3.6m
Canada-France-Hawaii Telescope (CFHT) and 6.5m Magellan-Clay telescope. Our
survey targets an unbiased sample of "outer halo" satellites (i.e.,
substructures having Galactocentric distances greater than 25 kpc) and includes
classical dSph galaxies, ultra-faint dwarfs, and remote globular clusters. We
combine deep, panoramic imaging for 44 satellites and archival
imaging for 14 additional objects (primarily obtained with the DECam instrument
as part of the Dark Energy Survey), to measure photometric and structural
parameters for 58 outer halo satellites. This is the largest and most uniform
analysis of Milky Way satellites undertaken to date and represents roughly
three quarters (72\%) of all known outer halo satellites. We use
a maximum-likelihood method to fit four density laws to each object in our
survey: exponential, Plummer, King and Sersic models. We examine systematically
the isodensity contour maps and color magnitude diagrams for each of our
program objects, present a comparison with previous results, and tabulate our
best-fit photometric and structural parameters, including ellipticities,
position angles, effective radii, Sersic indices, absolute magnitudes, and
surface brightness measurements. We investigate the distribution of outer halo
satellites in the size-magnitude diagram, and show that the current sample of
outer halo substructures spans a wide range in effective radius, luminosity and
surface brightness, with little evidence for a clean separation into star
cluster and galaxy populations at the faintest luminosities and surface
brightnesses.Comment: Accepted for publication in Ap
A Magellan M2FS Spectroscopic Survey of Galaxies at 5.5<z<6.8: Program Overview and a Sample of the Brightest Lyman-alpha Emitters
We present a spectroscopic survey of high-redshift, luminous galaxies over
four square degrees on the sky, aiming to build a large and homogeneous sample
of Ly emitters (LAEs) at and 6.5, and Lyman-break
galaxies (LBGs) at . The fields that we choose to observe are
well-studied, such as SXDS and COSMOS. They have deep optical imaging data in a
series of broad and narrow bands, allowing efficient selection of galaxy
candidates. Spectroscopic observations are being carried out using the
multi-object spectrograph M2FS on the Magellan Clay telescope. M2FS is
efficient to identify high-redshift galaxies, owing to its 256 optical fibers
deployed over a circular field-of-view 30 arcmin in diameter. We have observed
square degrees. When the program is completed, we expect to identify
more than 400 bright LAEs at and 6.5, and a substantial number of
LBGs at . This unique sample will be used to study a variety of galaxy
properties and to search for large protoclusters. Furthermore, the statistical
properties of these galaxies will be used to probe cosmic reionization. We
describe the motivation, program design, target selection, and M2FS
observations. We also outline our science goals, and present a sample of the
brightest LAEs at and 6.5. This sample contains 32 LAEs with
Ly luminosities higher than 10 erg s. A few of them reach
erg s, comparable to the two most luminous LAEs
known at , `CR7' and `COLA1'. These LAEs provide ideal targets to study
extreme galaxies in the distant universe.Comment: 18 pages, 11 figures, Accepted for publication in The Astrophysical
Journa
Signatures of stellar accretion in MaNGA early-type galaxies
The late assembly of massive galaxies is thought to be dominated by stellar accretion in their outskirts (beyond 2 effective radii Re) due to dry, minor galaxy mergers. We use observations of 1010 passive early-type galaxies (ETGs) within z10^{11}Msun ETGs. This is a signature of stellar accretion. Based on a toy model for stellar metallicity profiles, we infer the ex-situ stellar mass fraction in ETGs as a function of M and galactocentric radius. We find that ex-situ stars at 2Re make up 20% of the projected stellar mass of M10^{11.5}Msun ETGs
A Magellan M2FS Spectroscopic Survey of Galaxies at 5.5 < z < 6.8: Program Overview and a Sample of the Brightest Lya Emitters
We present a spectroscopic survey of high-redshift, luminous galaxies over four square degrees on the sky, aiming to build a large and homogeneous sample of Lyα emitters (LAEs) at and 6.5, and Lyman-break galaxies (LBGs) at . The fields that we choose to observe are well studied, such as by the Subaru XMM-Newton Deep Survey and COSMOS. They have deep optical imaging data in a series of broad and narrow bands, allowing for the efficient selection of galaxy candidates. Spectroscopic observations are being carried out using the multi-object spectrograph M2FS on the Magellan Clay telescope. M2FS is efficient enough to identify high-redshift galaxies, owing to its 256 optical fibers deployed over a circular field of view in diameter. We have observed ~2.5 square degrees. When the program is completed, we expect to identify more than 400 bright LAEs at and 6.5, and a substantial number of LBGs at . This unique sample will be used to study a variety of galaxy properties and to search for large protoclusters. Furthermore, the statistical properties of these galaxies will be used to probe cosmic reionization. We describe the motivation, program design, target selection, and M2FS observations. We also outline our science goals, and present a sample of the brightest LAEs at and 6.5. This sample contains 32 LAEs with Lyα luminosities higher than 1043 erg s−1. A few of them reach ≥3 × 1043 erg s−1, comparable to the two most luminous LAEs known at , "CR7" and "COLA1." These LAEs provide ideal targets to study extreme galaxies in the distant universe
Recommended from our members
SDSS-IV MaNGA: How the Stellar Populations of Passive Central Galaxies Depend on Stellar and Halo Mass
Abstract
We analyze spatially resolved and co-added SDSS-IV MaNGA spectra with signal-to-noise ratio ∼100 from 2200 passive central galaxies (z ∼ 0.05) to understand how central galaxy assembly depends on stellar mass (M
*) and halo mass (M
h
). We control for systematic errors in M
h
by employing a new group catalog from Tinker and the widely used Yang et al. catalog. At fixed M
*, the strengths of several stellar absorption features vary systematically with M
h
. Completely model-free, this is one of the first indications that the stellar populations of centrals with identical M
* are affected by the properties of their host halos. To interpret these variations, we applied full spectral fitting with the code alf. At fixed M
*, centrals in more massive halos are older, show lower [Fe/H], and have higher [Mg/Fe] with 3.5σ confidence. We conclude that halos not only dictate how much M
* galaxies assemble but also modulate their chemical enrichment histories. Turning to our analysis at fixed M
h
, high-M
* centrals are older, show lower [Fe/H], and have higher [Mg/Fe] for M
h
> 1012
h
−1
M
⊙ with confidence >4σ. While massive passive galaxies are thought to form early and rapidly, our results are among the first to distinguish these trends at fixed M
h
. They suggest that high-M
* centrals experienced unique early formation histories, either through enhanced collapse and gas fueling or because their halos were early forming and highly concentrated, a possible signal of galaxy assembly bias
SDSS-IV MaNGA: How the stellar populations of passive central galaxies depend on stellar and halo mass
We analyze spatially resolved and co-added SDSS-IV MaNGA spectra with
signal-to-noise ~100 from 2200 passive central galaxies (z~0.05) to understand
how central galaxy assembly depends on stellar mass (M*) and halo mass (Mh). We
control for systematic errors in Mh by employing a new group catalog from
Tinker (2020a,b) and the widely-used Yang et al. (2007) catalog. At fixed M*,
the strength of several stellar absorption features varies systematically with
Mh. Completely model-free, this is one of the first indications that the
stellar populations of centrals with identical M* are affected by the
properties of their host halos. To interpret these variations, we applied full
spectral fitting with the code alf. At fixed M*, centrals in more massive halos
are older, show lower [Fe/H], and have higher [Mg/Fe] with 3.5 sigma
confidence. We conclude that halos not only dictate how much M* galaxies
assemble, but also modulate their chemical enrichment histories. Turning to our
analysis at fixed Mh, high-M* centrals are older, show lower [Fe/H], and have
higher [Mg/Fe] for Mh>10^{12}Msun/h with confidence > 4 sigma. While massive
passive galaxies are thought to form early and rapidly, our results are among
the first to distinguish these trends at fixed Mh. They suggest that high-M*
centrals experienced unique early formation histories, either through enhanced
collapse and gas fueling, or because their halos were early-forming and highly
concentrated, a possible signal of galaxy assembly bias.Comment: Accepted for publication in ApJ. 28 pages and 12 figure