39 research outputs found
Scale Length of Disk Galaxies
As a part of a Euro-VO research initiative, we have undertaken a programme
aimed at studying the scale length of 54909 Sa-Sd spiral galaxies from the SDSS
DR6 catalogue. We have retrieved u,g,r,i,z-band images for all galaxies in
order to derive the light profiles. We also calculate asymmetry parameters to
select non-disturbed disks for which we will derive exponential disk scale
lengths. As images in different bands probe different optical depths and
stellar populations, it is likely that a derived scale length value should
depend on waveband, and our goal is to use the scale length variations with
band pass, inclination, galaxy type, redshift, and surface brightness, in order
to better understand the nature of spiral galaxies.Comment: Invited talk at the workshop "Multiwavelegth Astronomy and Virtual
Observatory" at ESA/ESAC in december 200
Revised SWIRE photometric redshifts
We have revised the Spitzer Wide-Area Infrared Extragalactic survey (SWIRE) Photometric
Redshift Catalogue to take account of new optical photometry in several of the SWIRE areas,
and incorporating Two Micron All Sky Survey (2MASS) and UKIRT Infrared Deep Sky
Survey (UKIDSS) near-infrared data. Aperture matching is an important issue for combining
near-infrared and optical data, and we have explored a number of methods of doing this.
The increased number of photometric bands available for the redshift solution results in
improvements both in the rms error and, especially, in the outlier rate.
We have also found that incorporating the dust torus emission into the quasi-stellar object
(QSO) templates improves the performance for QSO redshift estimation. Our revised redshift
catalogue contains over 1 million extragalactic objects, of which 26 288 are QSOs.Web of Scienc
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() ÂŒ A1 with A ÂŒ (0:6 0:3) ; 10 3; ÂŒ 2:03 0:10. With a fixed slope of ÂŒ 1:8, we obtain an amplitude of A ÂŒ (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 â 0:75, and this allows us to obtain an estimate of the three-dimensional correlation function (r), for which we find r0 ÂŒ 4:4 0:1 h 1 Mpc
Galaxy Clustering in Far-Infrared SWIRE Fields
We present measurements of galaxy clustering detected in the six
SWIRE fields in all MIPS channels at 24, 70, and 160 microns. The measurements
include the low-order 2-point angular correlation functions, and high-order
probes including probability distribution functions and RĂ©nyi information
Understanding Infrared Galaxy Populations: the SWIRE Legacy Survey
We discuss spectral energy distributions, photometric redshifts, redshift
distributions, luminosity functions, source-counts and the far infrared to
optical luminosity ratio for sources in the SWIRE Legacy Survey. The spectral
energy distributions of selected SWIRE sources are modelled in terms of a
simple set of galaxy and quasar templates in the optical and near infrared, and
with a set of dust emission templates (cirrus, M82 starburst, Arp 220
starburst, and AGN dust torus) in the mid infrared. The optical data, together
with the IRAC 3.6 and 4.5 mu data, have been used to determine photometric
redshifts. For galaxies with known spectroscopic redshifts there is a notable
improvement in the photometric redshift when the IRAC data are used, with a
reduction in the rms scatter from 10% in (1+z) to 5%. While further
spectroscopic data are needed to confirm this result, the prospect of
determining good photometric redshifts for the 2 million extragalactic objects
in SWIRE is excellent. The distribution of the different infrared sed types in
the L{ir}/L{opt} versus L{ir} plane, where L{ir} and L{opt} are the infrared
and optical bolometric luminosities, is discussed. Source-counts at 24, 70 and
160 mu are discussed, and luminosity functions at 3.6 and 24 mu are presented.Comment: 8 pages, 14 figures, to appear in proceedings of 'Spitzer IR
Diagnostics Conference, Nov 14-16, 2005
Hyper-luminous Reddened Broad-Line Quasars at z~2 from the VISTA Hemisphere Survey and WISE All Sky Survey
We present the first sample of spectroscopically confirmed heavily reddened
broad-line quasars selected using the new near infra-red VISTA Hemisphere
Survey and WISE All-Sky Survey. Observations of four candidates with (J-K)>2.5
and K<=16.5 over ~180 sq deg, leads to confirmation that two are highly
dust-reddened broad-line Type 1 quasars at z~2. The typical dust extinctions
are AV ~ 2-2.5 mags. We measure black-hole masses of ~10^9 M0 and extinction
corrected bolometric luminosities of ~10^47 erg/s, making these among the
brightest Type 1 quasars currently known. Despite this, these quasars lie well
below the detection limits of wide-field optical surveys like the SDSS with iAB
> 22. We also present WISE photometry at 3--22um, for our full sample of
spectroscopically confirmed reddened quasars including those selected from the
UKIDSS Large Area Survey (Banerji et al. 2012a). We demonstrate that the
rest-frame infrared SEDs of these reddened quasars are similar to UV-luminous
Type 1 quasars with significant hot dust emission and starburst quasar hosts
like Mrk231. The average 12um flux density of our reddened quasars is similar
to that of the recently discovered HyLIRG WISE1814+3412 (z=2.452) at similar
redshifts, with two of our reddened quasars also having comparable 22um flux
densities to this extreme HyLIRG. These optically faint, heavily reddened
broad-line quasars are therefore among the most mid infrared luminous galaxies
at z~2, now being discovered using WISE.Comment: 5 pages, MNRAS Letters, in press, Full photometric catalogue
available in online version of manuscript and at
http://www.ast.cam.ac.uk/~mbanerji/VHSWISE/redqso_vhs_wise_photom.pd
Detailed modelling of a large sample of Herschel sources in the Lockman Hole: identification of cold dust and of lensing candidates through their anomalous SEDs
We have studied in detail a sample of 967 SPIRE sources with 5Ï detections at 350 and 500 ÎŒm and associations with Spitzer-SWIRE 24 ÎŒm galaxies in the HerMES-Lockman survey area, fitting theirmid- and far-infrared, and submillimetre, spectral energy distributions (SEDs) in an automatic search with a set of six infrared templates. For almost 300 galaxies,we havemodelled their SEDs individually to ensure the physicality of the fits. We confirm the need for the new cool and cold cirrus templates, and also of the young starburst template, introduced in earlier work. We also identify 109 lensing candidates via their anomalous SEDs and provide a set of colourâredshift constraints which allow lensing candidates to be identified from combined Herschel and Spitzer data. The picture that emerges of the submillimetre galaxy population is complex, comprising ultraluminous and hyperluminous starbursts, lower luminosity galaxies dominated by interstellar dust emission, lensed galaxies and galaxies with surprisingly cold (10â13 K) dust. 11 per cent of 500 ÎŒm selected sources are lensing candidates. 70 per cent of the unlensed sources are ultraluminous infrared galaxies and 26 per cent are hyperluminous. 34 per cent are dominated by optically thin interstellar dust (âcirrusâ) emission, but most of these are due to cooler dust than is characteristic of our Galaxy. At the highest infrared luminosities we see SEDs dominated by M82, Arp 220 and young starburst types, in roughly equal proportions
Parametric modelling of the 3.6um to 8um colour distributions of galaxies in the SWIRE Survey
We fit a parametric model comprising a mixture of multi-dimensional Gaussian
functions to the 3.6 to 8um colour and optical photo-z distribution of galaxy
populations in the ELAIS-N1 and Lockman Fields of SWIRE. For 16,698 sources in
ELAIS-N1 we find our data are best modelled (in the sense of the Bayesian
Information Criterion) by the sum of four Gaussian distributions or modes (C_a,
C_b, C_c and C_d). We compare the fit of our empirical model with predictions
from existing semi-analytic and phenomological models. We infer that our
empirical model provides a better description of the mid-infrared colour
distribution of the SWIRE survey than these existing models. This colour
distribution test is thus a powerful model discriminator and complementary to
comparisons of number counts. We use our model to provide a galaxy
classification scheme and explore the nature of the galaxies in the different
modes of the model. C_a consists of dusty star-forming systems such as ULIRG's.
Low redshift late-type spirals are found in C_b, where PAH emission dominates
at 8um. C_c consists of dusty starburst systems at intermediate redshifts. Low
redshift early-type spirals and ellipticals dominate C_d. We thus find a
greater variety of galaxy types than one can with optical photometry alone.
Finally we develop a new technique to identify unusual objects, and find a
selection of outliers with very red IRAC colours. These objects are not
detected in the optical, but have very strong detections in the mid-infrared.
These sources are modelled as dust-enshrouded, strongly obscured AGN, where the
high mid-infrared emission may either be attributed to dust heated by the AGN
or substantial star-formation. These sources have z_ph ~ 2-4, making them
incredibly infrared luminous, with a L_IR ~ 10^(12.6-14.1) L_sun.Comment: 44 pages, 10 figures, 6 tables. Accepted for publication in the
Astronomical Journa
High-Redshift QSOs in the SWIRE Survey and the z~3 QSO Luminosity Function
We use a simple optical/infrared (IR) photometric selection of high-redshift
QSOs that identifies a Lyman Break in the optical photometry and requires a red
IR color to distinguish QSOs from common interlopers. The search yields 100 z~3
(U-dropout) QSO candidates with 19<r'<22 over 11.7 deg^2 in the ELAIS-N1 (EN1)
and ELAIS-N2 (EN2) fields of the Spitzer Wide-area Infrared Extragalactic
(SWIRE) Legacy Survey. The z~3 selection is reliable, with spectroscopic
follow-up of 10 candidates confirming they are all QSOs at 2.83<z<3.44. We find
that our z~4$ (g'-dropout) sample suffers from both unreliability and
incompleteness but present 7 previously unidentified QSOs at 3.50<z<3.89.
Detailed simulations show our z~3 completeness to be ~80-90% from 3.0<z<3.5,
significantly better than the ~30-80% completeness of the SDSS at these
redshifts. The resulting luminosity function extends two magnitudes fainter
than SDSS and has a faint end slope of beta=-1.42 +- 0.15, consistent with
values measured at lower redshift. Therefore, we see no evidence for evolution
of the faint end slope of the QSO luminosity function. Including the SDSS QSO
sample, we have now directly measured the space density of QSOs responsible for
~70% of the QSO UV luminosity density at z~3. We derive a maximum rate of HI
photoionization from QSOs at z~3.2, Gamma = 4.8x10^-13 s^-1, about half of the
total rate inferred through studies of the Ly-alpha forest. Therefore,
star-forming galaxies and QSOs must contribute comparably to the
photoionization of HI in the intergalactic medium at z~3.Comment: Accepted for publication in ApJ. emulateapj format. 23 pages, 17
figure