59 research outputs found
Infrared-Faint Radio Sources: A New Population of High-redshift Radio Galaxies
We present a sample of 1317 Infrared-Faint Radio Sources (IFRSs) that, for
the first time, are reliably detected in the infrared, generated by
cross-correlating the Wide-Field Infrared Survey Explorer (WISE) all-sky survey
with major radio surveys. Our IFRSs are brighter in both radio and infrared
than the first generation IFRSs that were undetected in the infrared by the
Spitzer Space Telescope. We present the first spectroscopic redshifts of IFRSs,
and find that all but one of the IFRSs with spectroscopy has z > 2. We also
report the first X-ray counterparts of IFRSs, and present an analysis of radio
spectra and polarization, and show that they include Gigahertz-Peaked Spectrum,
Compact Steep Spectrum, and Ultra-Steep Spectrum sources. These results,
together with their WISE infrared colours and radio morphologies, imply that
our sample of IFRSs represents a population of radio-loud Active Galactic
Nuclei at z > 2. We conclude that our sample consists of lower-redshift
counterparts of the extreme first generation IFRSs, suggesting that the fainter
IFRSs are at even higher redshift.Comment: 23 pages, 17 figures. Submitted to MNRA
Angular clustering of galaxies at 3.6 microns from the Spitzer Wide-area Infrared Extragalactic (SWIRE) Survey
We present the first analysis of large-scale clustering from the Spitzer Wide-area Infrared Extragalactic legacy survey (SWIRE). We compute the angular correlation function of galaxies selected to have 3.6 m fluxes brighter than 32 Jy in three fields totaling 2 deg2 in area. In each field we detect clustering with a high level of significance. The amplitude and slope of the correlation function is consistent between the three fields and is modeled as w() ¼ A1 with A ¼ (0:6 0:3) ; 10 3; ¼ 2:03 0:10. With a fixed slope of ¼ 1:8, we obtain an amplitude of A ¼ (1:7 0:1) ; 10 3. Assuming an equivalent depth of K 18:7 mag we find that our errors are smaller but our results are consistent with existing clustering measurements in K-band surveys and with stable clustering models. We estimate our median redshift z ’ 0:75, and this allows us to obtain an estimate of the three-dimensional correlation function (r), for which we find r0 ¼ 4:4 0:1 h 1 Mpc
The Local Volume HI Survey: star formation properties
We built a multi-wavelength dataset for galaxies from the Local Volume HI
Survey (LVHIS), which comprises 82 galaxies. We also select a sub-sample of ten
large galaxies for investigating properties in the galactic outskirts. The
LVHIS sample covers nearly four orders of magnitude in stellar mass and two
orders of magnitude in HI mass fraction (fHI). The radial distribution of HI
gas with respect to the stellar disc is correlated with fHI but with a large
scatter. We confirm the previously found correlations between the total HI mass
and star formation rate (SFR), and between HI surface densities and SFR surface
densities beyond R25. However, the former correlation becomes much weaker when
the average surface densities rather than total mass or rate are considered,
and the latter correlation also becomes much weaker when the effect of stellar
mass is removed or controlled. Hence the link between SFR and HI is
intrinsically weak in these regions, consistent with what was found on kpc
scales in the galactic inner regions. We find a strong correlation between the
SFR surface density and the stellar mass surface density, which is consistent
with the star formation models where the gas is in quasi-equilibrium with the
mid-plane pressure. We find no evidence for HI warps to be linked with
decreasing star forming efficiencies.Comment: 31 pages, 20 figures, 4 tables. Accepted for publication at MNRA
Near-Infrared Synchrotron Emission from Cas A
High energy observations of Cas A suggested the presence of synchrotron
radiation, implying acceleration of cosmic rays by young supernova remnants. We
detect synchrotron emission from Cas A in the near-infrared using Two Micron
All Sky Survey (2MASS) and Palomar 200 inch PFIRCAM observations. The remnant
is detected in J, H, and Ks bands, with Ks band brightest and J faint. In the J
and H bands, bright [Fe II] lines (1.24um and 1.64um) are detected
spectroscopically. The Palomar observations include Ks continuum, narrow-band
1.64um (centered on [Fe II]) and 2.12um (centered on H2(1-0)) images. While the
narrow-band 1.64um image shows filamentary and knotty structures, similar to
the optical image, the Ks image shows a relatively smooth, diffuse shell,
remarkably similar to the radio image. The broad-band near-infrared fluxes of
Cas A are generally consistent with, but a few tens of percent higher than, an
extrapolation of the radio fluxes. The hardening to higher frequencies is
possibly due to nonlinear shock acceleration and/or spectral index variation
across the remnant. We show evidence of spectral index variation. The presence
of near-infrared synchrotron radiation requires the roll-off frequency to be
higher than 1.5e14 Hz, implying that electrons are accelerated to energies of
at least 0.2 TeV. The morphological similarity in diffuse emission between the
radio and Ks band images implies that synchrotron losses are not dominant. Our
observations show unambiguous evidence that the near-infrared Ks band emission
of Cas A is from synchrotron emission by accelerated cosmic-ray electrons.Comment: accepted by Ap
2MTF VI. Measuring the velocity power spectrum
We present measurements of the velocity power spectrum and constraints on the
growth rate of structure , at redshift zero, using the peculiar
motions of 2,062 galaxies in the completed 2MASS Tully-Fisher survey (2MTF). To
accomplish this we introduce a model for fitting the velocity power spectrum
including the effects of non-linear Redshift Space Distortions (RSD), allowing
us to recover unbiased fits down to scales without
the need to smooth or grid the data. Our fitting methods are validated using a
set of simulated 2MTF surveys. Using these simulations we also identify that
the Gaussian distributed estimator for peculiar velocities of
\cite{Watkins2015} is suitable for measuring the velocity power spectrum, but
sub-optimal for the 2MTF data compared to using magnitude fluctuations , and that, whilst our fits are robust to a change in fiducial cosmology,
future peculiar velocity surveys with more constraining power may have to
marginalise over this. We obtain \textit{scale-dependent} constraints on the
growth rate of structure in two bins, finding in the ranges . We also find consistent results using four
bins. Assuming scale-\textit{independence} we find a value , a measurement of the growth rate. Performing
a consistency check of General Relativity (GR) and combining our results with
CMB data only we find , a remarkable constraint
considering the small number of galaxies. All of our results are completely
independent of the effects of galaxy bias, and fully consistent with the
predictions of GR (scale-independent and ).Comment: 18 pages, 14 figures, 3 tables. Accepted for publication in MNRA
Azimuthal and Kinematic Segregation of Neutral and Molecular Gas in Arp 118: The Yin-Yang Galaxy NGC 1144
We present new high-resolution HI observations of the disk of the collisional
infrared luminous (L L_{\sun}) galaxy NGC 1144,
which reveal an apparent large-scale azimuthal and kinematic segregation of
neutral hydrogen relative to the molecular gas distribution. Even among
violently collisional galaxies, the CO/HI asymmetry in NGC 1144 is unusual,
both in the inner regions, and in the outer disk. We suggest that we are
observing Arp 118 at a special moment, shortly after a high-speed collision
between NGC 1144 and its elliptical companion NGC 1143. HI emission with an
average molecular fraction f 0.5 is observed on one side (NW) of
the rotating disk of NGC 1144, while the other side (SE) is dominated by dense
molecular complexes in which f is almost unity. The interface region
between the warm-- and cool--cloud dominated regions, lies on a deep
spiral-like dust-lane which we identify as a shock-wave responsible for the
relative shift in the dominance of HI and H gas. A strong shock being fed
by diffuse HI clouds with unusually large ( 400 km s) rotational
velocities can explain: 1) the CO/HI asymmetries, 2) a large velocity jump (185
km s) across the arm as measured by HI absorption against a radio bright
continuum source which straddles the arm, and 3) the asymmetric distribution of
star formation and off-nuclear molecular gas resulting from likely streaming
motions associated with the strong-shock. The new results provide for the first
time a coherent picture of Arp 118's many peculiarities, and underlines the
potentially complex changes in the gas-phase that can accompany large
gravitational perturbations of gas-rich galaxies.Comment: 20 pages, two tables, 9 Figure
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