69 research outputs found
The Challenge to Large Optical Telescopes from X-ray Astronomy
In the ROSAT era of the mid-1990's, the problems facing deep X-ray surveys
could be largely solved with 10 m class telescopes. In the first decade of this
new millennium, with X-ray telescopes such as the Chandra X-ray Observatory and
XMM-Newton in operation, deep X-ray surveys are challenging 10 m telescopes.
For example, in the Chandra Deep Field surveys, approximately 30% of the X-ray
sources have optical counterparts fainter than R=25 (I=24).
This paper reviews current progress with 6-10 m class telescopes in following
up sources discovered in deep X-ray surveys, including results from several
X-ray surveys which have depended on telescopes such as Keck, VLT and HET.
Topics include the prospects for detecting extreme redshift (z>6) quasars and
the first detections of normal and starburst galaxies at cosmologically
interesting distances in the X-ray band.
X-ray astronomy can significantly bolster the science case for the next
generation of large aperture (30-100 m) ground-based telescopes and has already
provided targets for these large telescopes through the Chandra and XMM-Newton
surveys. The next generation of X-ray telescopes will continue to challenge
large optical telescopes; this review concludes with a discussion of prospects
from new X-ray missions coming into operation on a 5-30 year timescale.Comment: 15 pages, 6 figures, Invited review for SPIE conference "Science with
6-10 m Class Telescopes
Some Like It Hot: Linking Diffuse X-ray Luminosity, Baryonic Mass, and Star Formation Rate in Compact Groups of Galaxies
We present an analysis of the diffuse X-ray emission in 19 compact groups of
galaxies (CGs) observed with Chandra. The hottest, most X-ray luminous CGs
agree well with the galaxy cluster X-ray scaling relations in and
, even in CGs where the hot gas is associated with only the
brightest galaxy. Using Spitzer photometry, we compute stellar masses and
classify HCGs 19, 22, 40, and 42 and RSCGs 32, 44, and 86 as fossil groups
using a new definition for fossil systems that includes a broader range of
masses. We find that CGs with total stellar and HI masses
M are often X-ray luminous, while lower-mass CGs only sometimes exhibit
faint, localized X-ray emission. Additionally, we compare the diffuse X-ray
luminosity against both the total UV and 24 m star formation rates of each
CG and optical colors of the most massive galaxy in each of the CGs. The most
X-ray luminous CGs have the lowest star formation rates, likely because there
is no cold gas available for star formation, either because the majority of the
baryons in these CGs are in stars or the X-ray halo, or due to gas stripping
from the galaxies in CGs with hot halos. Finally, the optical colors that trace
recent star formation histories of the most massive group galaxies do not
correlate with the X-ray luminosities of the CGs, indicating that perhaps the
current state of the X-ray halos is independent of the recent history of
stellar mass assembly in the most massive galaxies.Comment: 20 pages, 7 figures, accepted for publication in Ap
Evidence for Elevated X-ray Emission in Local Lyman Break Galaxy Analogs
In this paper, we study the relationship between the 2-10 keV X-ray
luminosity (L_X), assumed to originate from X-ray binaries (XRBs), and star
formation rate (SFR) in UV-selected z<0.1 Lyman break analogs (LBAs). We
present Chandra observations for four new GALEX-selected LBAs. Including
previously studied LBAs, Haro 11 and VV 114, we find that LBAs demonstrate
L_X/SFR ratios that are elevated by ~1.5sigma compared to local galaxies,
similar to the ratios found for stacked LBGs in the early Universe (z>2). We
show that these LBAs are unlikely to harbor AGN, based on their optical and
X-ray spectra and the spatial distribution of the X-rays in three spatially
extended cases. We expect that high-mass X-ray binaries (HMXBs) dominate the
X-ray emission in these galaxies, based on their high specific SFRs
(sSFRs=SFR/M* > 10^{-9}/yr), which suggest the prevalence of young stellar
populations. Since both LBAs and LBGs have lower dust attenuations and
metallicities compared to similar samples of more typical local galaxies, we
investigate the effects of dust extinction and metallicity on the L_X/SFR for
the broader population of galaxies with high sSFRs (>10^{-10}/yr). The
estimated dust extinctions (corresponding to column densities of
N_H<10^{22}/cm^2) are expected to have insignificant effects on observed
L_X/SFR ratio for the majority of galaxy samples. We find that the observed
relationship between L_X/SFR and metallicity appears consistent with
theoretical expectations from X-ray binary population synthesis models.
Therefore, we conclude that lower metallicities, related to more luminous HMXBs
such as ultraluminous X-ray sources (ULXs), drive the elevated L_X/SFR observed
in our sample of z<0.1 LBAs. The relatively metal-poor, active mode of star
formation in LBAs and distant z>2 LBGs may yield higher total HMXB luminosity
than found in typical galaxies in the local Universe.Comment: 11 pages, 7 figures, Submitted to ApJ (references updated in v2
What dominates the X-ray emission of normal galaxies?
X-ray surveys of normal galaxies, i.e. those that do not host actively supermassive black holes, have revealed important information on the nature of accreting stellar-mass compact objects (neutron stars and black holes), constraints on populations of possible intermediate-mass black holes (102-5 M ☉), and on the reservoir of materials in the hot interstellar medium of the most massive galaxies. Here we summarize briefly the results of Chandra and NuSTAR surveys of several samples of galaxies covered during the 2015 IAU General Assembly. This includes a comprehensive study of six nearby starburst galaxies by the NuSTAR mission, of high-redshift galaxies from the 6 Ms Chandra Deep Field South for which evolutionary trends in X-ray emission over cosmic time have been measured, of collisional ring galaxies which are excellent local environments for studying intermediate-mass black holes and of elliptical galaxies which are ideal for study of the hot gas reservoirs containing the effects of stellar and AGN feedback
The Infrared Properties of Hickson Compact Groups
Compact groups of galaxies provide a unique environment to study the
mechanisms by which star formation occurs amid continuous gravitational
encounters. We present 2MASS (JHK), Spitzer IRAC (3.5-8 micron) and MIPS (24
micron) observations of a sample of twelve Hickson Compact Groups (HCGs 2, 7,
16, 19, 22, 31, 42, 48, 59, 61, 62, and 90) that includes a total of 45
galaxies. The near-infrared colors of the sample galaxies are largely
consistent with being dominated by slightly reddened normal stellar
populations. Galaxies that have the most significant PAH and/or hot dust
emission (as inferred from excess 8 micron flux) also tend to have larger
amounts of extinction and/or K-band excess and stronger 24 micron emission, all
of which suggest ongoing star formation activity. We separate the twelve HCGs
in our sample into three types based on the ratio of the group HI mass to
dynamical mass. We find evidence that galaxies in the most gas-rich groups tend
to be the most actively star forming. Galaxies in the most gas-poor groups tend
to be tightly clustered around a narrow range in colors consistent with the
integrated light from a normal stellar population. We interpret these trends as
indicating that galaxies in gas-rich groups experience star formation and/or
nuclear actively until their neutral gas consumed, stripped, or ionized. The
galaxies in this sample exhibit a ``gap'' between gas-rich and gas-poor groups
in infrared color space that is sparsely populated and not seen in the Spitzer
First Look Survey sample. This gap may suggest a rapid evolution of galaxy
properties in response to dynamical effects. These results suggest that the
global properties of the groups and the local properties of the galaxies are
connected.Comment: 34 pages, 26 figures, accepted for publication in AJ, higher quality
images available in publicatio
Examining the Role of Environment in a Comprehensive Sample of Compact Groups
(Abridged) Compact groups, with their high number densities, small velocity
dispersions, and an interstellar medium that has not been fully processed,
provide a local analog to conditions of galaxy interactions in the earlier
universe. The frequent and prolonged gravitational encounters that occur in
compact groups affect the evolution of the constituent galaxies in a myriad of
ways, for example gas processing and star formation. Recently, a statistically
significant "gap" has been discovered mid-infrared IRAC colorspace of compact
group galaxies. This gap is not seen in field samples and is a new example of
how the compact group environment may affect the evolution of member galaxies.
In order to investigate the origin and nature of this gap, we have compiled a
sample of 49 compact groups. We find that a statistically significant deficit
of galaxies in this gap region of IRAC colorspace is persistant in this sample,
lending support to the hypothesis that the compact group environment inhibits
moderate SSFRs. We note a curvature in the colorspace distribution, which is
fully consistent with increasing dust temperature as the activity in a galaxy
increases. This full sample of 49 compact groups allows us to subdivide the
data according to physical properties of the groups. An analysis of these
subsamples indicates that neither projected physical diameter nor density show
a trend in colorspace within the values represented by this sample. We
hypothesize that the apparent lack of a trend is due to the relatively small
range of properties in this sample. Thus, the relative influence of stochastic
effects becomes dominant. We analyze spectral energy distributions of member
galaxies as a function of their location in colorspace and find that galaxies
in different regions of MIR colorspace contain dust with varying temperatures
and/or PAH emission.Comment: 24 pages, 13 figures. Accepted for publication in The Astronomical
Journa
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