91 research outputs found
A multi-wavelength analysis of Spitzer selected Coma Cluster galaxies: star formation rates and masses
We present a thorough study of the specific star formation rates for MIPS
24um selected galaxies in the Coma cluster. We build galaxy spectral energy
distributions using optical (u',g',r',i',z'), Near-infrared (J,H,Ks), and Mid
to Far-infrared (IRAC and MIPS) photometry. New and archival spectra confirm
210 cluster members. Subsequently, the total infrared luminosity, galaxy
stellar mass, and specific star formation rate for the members are determined
by measuring best fit templates. Using an array of complementary diagnostics,
we search for contaminating AGN, but find few. We compare obscured star
formation rates to unobscured rates derived from extinction-corrected H-alpha
emission line measurements. The agreement between these two values leads us to
conclude that there is no evidence for an additionally obscured component. In
our spectroscopic sample, complete to 80% for r' < 19.5, we find that all
starbursts are blue and are dwarfs, having masses < 10^9 solar masses.
Examining the location of these starbursts within the cluster, we confirm that
there is a lower fraction in the cluster core.Comment: 30pages, 16 figures, accepted to A
Spitzer observations of Abell 1763 - I: infrared and optical photometry
We present a photometric analysis of the galaxy cluster Abell 1763 at visible
and infrared wavelengths. Included are fully reduced images in r', J, H, and Ks
obtained using the Palomar 200in telescope, as well as the IRAC and MIPS images
from Spitzer. The cluster is covered out to approximately 3 virial radii with
deep 24um imaging (a 5? depth of 0.2 mJy). This same field of 40' by 40' is
covered in all four IRAC bands as well as the longer wavelength MIPS bands (70
and 160um). The r' imaging covers 0.8 deg2 down to 25.5 magnitudes, and
overlaps with most of the MIPS field of view. The J, H, Ks images cover the
cluster core and roughly half of the filament galaxies, which extend towards
the neighboring cluster, Abell 1770. This first, in a series of papers on Abell
1763, discusses the data reduction methods and source extraction techniques
used for each dataset. We present catalogs of infrared (IR) sources (with 24
and/or 70um emission) and their corresponding emission in the optical (u', g',
r', i', z'), and Near- to Far-IR (J, H, Ks, IRAC, and MIPS 160um). We provide
the catalogs and reduced images to the community through the NASA/IPAC Infrared
Science Archive (IRSA).Comment: 25 pages, 16 figure
Spitzer observations of Abell 1763 - II: Constraining the nature of activity in the cluster-feeding filament with VLA and XMM-Newton data
The Abell 1763 superstructure at z=0.23 contains the first galaxy filament to
be directly detected using mid-infrared observations. Our previous work has
shown that the frequency of starbursting galaxies, as characterized by 24{\mu}m
emission is much higher within the filament than at either the center of the
rich galaxy cluster, or the field surrounding the system. New VLA and
XMM-Newton data are presented here. We use the radio and X-ray data to examine
the fraction and location of active galaxies, both active galactic nuclei (AGN)
and starbursts. The radio far-infrared correlation, X-ray point source
location, IRAC colors, and quasar positions are all used to gain an
understanding of the presence of dominant AGN. We find very few MIPS-selected
galaxies that are clearly dominated by AGN activity. Most radio selected
members within the filament are starbursts. Within the supercluster, 3 of 8
spectroscopic members detected both in the radio and in the mid-infrared are
radio-bright AGN. They are found at or near the core of Abell 1763. The five
starbursts are located further along the filament. We calculate the physical
properties of the known wide angle tail (WAT) source which is the brightest
cluster galaxy (BCG) of Abell 1763. A second double lobe source is found along
the filament well outside of the virial radius of either cluster. The velocity
offset of the WAT from the X-ray centroid, and the bend of the WAT in the
intracluster medium (ICM) are both consistent with ram pressure stripping,
indicative of streaming motions along the direction of the filament. We
consider this as further evidence of the cluster-feeding nature of the galaxy
filament.Comment: 26 pages, 13 figures AJ, accepte
The Diverse Nature of Optical Emission Lines in Brightest Cluster Galaxies: IFU Observations of the Central Kiloparsecs
We present integral field spectroscopy of the nebular line emission in a
sample of 9 brightest cluster galaxies (BCGs). The sample was chosen to probe
both cooling flow and non-cooling flow clusters, as well as a range of cluster
X-ray luminosities. The line emission morphology and velocity gradients suggest
a great diversity in the properties of the line emitting gas. While some BGCs
show evidence for filamentary or patchy emission (Abell 1060, Abell 1668 and
MKW3s), others have extended emission (Abell 1204, Abell 2199), while still
others have centrally concentrated emission (Abell 2052). We examine diagnostic
line ratios to determine the dominant ionization mechanisms in each galaxy.
Most of the galaxies show regions with AGN-like spectra, however for two BCGs,
Abell 1060 and Abell 1204, the emission line diagnostics suggest regions which
can be described by the emission from young stellar populations. The diversity
of emission line properties in our sample of BCGs suggests that the emission
mechanism is not universal, with different ionization processes dominating
different systems. Given this diversity, there is no evidence for a clear
distinction of the emission line properties between cooling flow and
non-cooling flow BCGs. It is not always cooling flow BCGs which show emission
(or young stellar populations), and non-cooling flow BCGs which do not.Comment: 23 pages, 23 figures, accepted for publication in MNRAS. Full
resolution images are online http://web.ipac.caltech.edu/staff/louis
Close companions to Brightest Cluster Galaxies: Support for minor mergers and downsizing
We identify close companions of Brightest Cluster Galaxies (BCGs) for the
purpose of quantifying the rate at which these galaxies grow via mergers. By
exploiting deep photometric data from the CFHTLS, we probe the number of
companions per BCG (Nc) with luminosity ratios down to those corresponding to
potential minor mergers of 20:1. We also measure the average luminosity in
companions per galaxy (Lc). We find that Nc and Lc rise steeply with luminosity
ratio for both the BCGs, and a control sample of other bright, red, cluster
galaxies. The trend for BCGs rises more steeply, resulting in a larger number
of close companions. For companions within 50kpc of a BCG, Nc= 1.38+/-0.14 and
Lc=(2.14+/-0.31)x10^(10)L_sun and for companions within 50kpc of a luminosity
matched control sample of non-BCGs, Nc=0.87+/-0.08 and
Lc=(1.48+/-0.20)x10^(10)L_sun. This suggests that the BCGs are likely to
undergo more mergers compared to otherwise comparable luminous galaxies.
Additionally, compared to a local sample of luminous red galaxies, the more
distant sample presented in this study (with redshifts between 0.15-0.39,)
shows a higher Nc, suggesting the younger and smaller BCGs are still undergoing
hierarchical formation. Using the Millennium Simulations we model and estimate
the level of contamination due to unrelated cluster galaxies. The contamination
by interloping galaxies is 50% within projected separations of 50kpc, but
within 30kpc, 60% of identified companions are real physical companions. We
conclude that the luminosity of bound merger candidates down to luminosity
ratios of 20:1 could be adding as much as 10% to the mass of a typical BCG over
0.5Gyr at redshifts of z~0.3.Comment: 10 pages, 7 figures. Accepted and to be published in MNRA
Clocking the formation of today's largest galaxies: Wide field integral spectroscopy of Brightest Cluster Galaxies and their surroundings
The formation and evolution of local brightest cluster galaxies (BCGs) is
investigated by determining the stellar populations and dynamics from the
galaxy core, though the outskirts and into the intracluster light (ICL).
Integral spectroscopy of 23 BCGs observed out to 4 r_e is collected and high
signal-to-noise regions are identified. Stellar population synthesis codes are
used to determine the age, metallicity, velocity, and velocity dispersion of
stars within each region. The intracluster light (ICL) spectra are best modeled
with populations that are younger and less metal-rich than those of the BCG
cores. The average BCG core age of the sample is 13.3 2.8 Gyr and the
average metallicity is [Fe/H] = 0.30 0.09, whereas for the ICL the
average age is 9.23.5 Gyr and the average metallicity is [Fe/H] =
0.180.16. The velocity dispersion profile is seen to be rising or flat in
most of the sample (17/23), and those with rising values reach the value of the
host cluster's velocity dispersion in several cases. The most extended BCGs are
closest to the peak of the cluster's X-ray luminosity. The results are
consistent with the idea that the BCG cores and inner regions formed quickly
and long ago, with the outer regions and ICL forming more recently, and
continuing to assemble through minor merging. Any recent star formation in the
BCGs is a minor component, and is associated with the cluster cool core status.Comment: 22 pages, 21 figures, MNRAS, accepte
Cold, clumpy accretion onto an active supermassive black hole
Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales. The nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas. Recent theory and simulations instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds - a departure from the "hot mode" accretion model - although unambiguous observational support for this prediction remains elusive. Here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (redshift z=0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma. Under the right conditions, thermal instabilities can precipitate from this hot gas, producing a rain of cold clouds that fall toward the galaxy's centre, sustaining star formation amid a kiloparsec-scale molecular nebula that inhabits its core. The observations show that these cold clouds also fuel black hole accretion, revealing "shadows" cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole in the galaxy centre, which serves as a bright backlight. Corroborating evidence from prior observations of warmer atomic gas at extremely high spatial resolution, along with simple arguments based on geometry and probability, indicate that these clouds are within the innermost hundred parsecs of the black hole, and falling closer towards it
Co-ordinated Role of TLR3, RIG-I and MDA5 in the Innate Response to Rhinovirus in Bronchial Epithelium
The relative roles of the endosomal TLR3/7/8 versus the intracellular RNA helicases RIG-I and MDA5 in viral infection is much debated. We investigated the roles of each pattern recognition receptor in rhinovirus infection using primary bronchial epithelial cells. TLR3 was constitutively expressed; however, RIG-I and MDA5 were inducible by 8–12 h following rhinovirus infection. Bronchial epithelial tissue from normal volunteers challenged with rhinovirus in vivo exhibited low levels of RIG-I and MDA5 that were increased at day 4 post infection. Inhibition of TLR3, RIG-I and MDA5 by siRNA reduced innate cytokine mRNA, and increased rhinovirus replication. Inhibition of TLR3 and TRIF using siRNA reduced rhinovirus induced RNA helicases. Furthermore, IFNAR1 deficient mice exhibited RIG-I and MDA5 induction early during RV1B infection in an interferon independent manner. Hence anti-viral defense within bronchial epithelium requires co-ordinated recognition of rhinovirus infection, initially via TLR3/TRIF and later via inducible RNA helicases
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