New Nature Letter: Near-infrared background anisotropies from diffuse intrahalo light of galaxies

Abstract - Unresolved near-infrared background anisotropies are expected to have contributions from the earliest galaxies during reionization and faint, dwarf galaxies at intermediate redshifts. Previous measurements were unable to conclusively pinpoint the dominant origin because they did not sample spatial scales that were sufficiently large to distinguish between these two possibilities. Here we report a measurement of the anisotropy power spectrum from sub-arcminute to one degree angular scales and find the clustering amplitude to be larger than the model predictions involving the two existing explanations. As the shot-noise level of the power spectrum is consistent with that expected from faint galaxies, a new source population on the sky is not necessary to explain the observations. A physical mechanism that increases the clustering amplitude, however, is needed. Motivated by recent results related to the extended stellar light profile in dark matter halos, we consider the possibility that the fluctuations originate from diffuse intrahalo stars of all galaxies. We find that the measured power spectrum can be explained by an intrahalo light fraction of 0.07 to 0.2% relative to the total luminosity in dark matter halos of 109 to 1012 solar masses at redshifts of ∼1 to 4.

For the Nature article see here.

Prof. Andrea Ferrara from SNS, Italy wrote the introductory News and Views article that also appears in Nature.

Scientists who are interested in the data related to this work can obtain the data from Spitzer Heritage Archive under PID 40839 (SDWFS).

Press articles related to this work available from UCI, UCLA, JPL, NASA, INAFNBCNews, Universe Today

The angular power spectrum of the unresolved near-IR background. The total power spectrum of SDWFS at 3.6 μm as a function of the multipole moment. The two shaded regions show the expected contribution from z > 6 galaxies and low-redshift galaxies based on two model predictions in the literature. The lines shows a diffuse intrahalo light model where we show the signal in terms of the total (solid), one (dashed-dotted) and two (dotted) halo terms.

The intrahalo light fraction from diffuse stars as a function of the halo mass. The dark and light blue shaded regions show the 95% and 68% range of fIHL relative to the total luminosity of the dark matter halos as a function of the halo mass from an analytical prediction, valid for fIHL > 4×10−4 and M > 5×1010 M⊙ and at z = 0.

The image on the left show a portion of our sky in infrared light, called the Boötes field, while the image on the right shows a mysterious, background infrared glow captured by NASA's Spitzer Space Telescope in the same region of sky. Researchers using Spitzer were able to detect this background glow, which spreads across the whole sky, by masking out light from galaxies and other known sources of light (the masks are the gray, blotchy marks). The scientists say that this light is coming from stray stars that were torn away from galaxies. When galaxies tangle and merge -- a natural stage of galaxy growth -- stars often get kicked out in the process. The stars are too faint to be seen individually, but Spitzer may be seeing their collective glow. Image credit: NASA/JPL-Caltech/UC Irvine

New research from scientists using NASA's Spitzer Space Telescope suggests that a mysterious infrared glow across our whole sky is coming from stray stars torn from galaxies. When galaxies grow, they merge and become gravitationally tangled in a violent process that results in streams of stars being ripped away from the galaxies. Such streams, called tidal tails, can be seen in the artist's concept. Scientists say that Spitzer is picking up the collective glow of stars such as these, which linger in the spaces between galaxies. This artwork is adapted, in part, from galaxy images obtained from the NASA/ESA Hubble Space Telescope. Image credit: NASA/JPL-Caltech

The European science magazine International Innovation recently published an article about some of our work! Check it out here.
International Innovation is the leading global dissemination resource for the wider scientific, technology and research communities, dedicated to disseminating the latest science, research and technological innovations on a global level. More information and a complimentary subscription offer to the publication can be found at:

Local massive galaxies are formed in violent starbursts

A new paper, to be published by MNRAS on January 26th, uses clustering to measure the mass of the dark matter halos that distant submillimeter galaxies reside in. Submillimeter galaxies are undergoing extreme bursts of star-formation, forming hundreds of new stars each year, but these violent starbursts are rapidly quenched.

The new results suggest that these extreme starbursts are shut-down by quasars, that is activity in the massive black holes that reside in the centers of the galaxies. The submillimeter galaxies then passively evolve into massive galaxies in the local Universe.

More information can be found in the ESO press release, or in the scientific paper, which is authored by Ryan Hickox, Julie Wardlow, Ian Smail, A. D. Myers, D. M. Alexander, A. L. R. Danielson, J. P. Stott, S. C. Chapman, K. E. K. Coppin, J. S. Dunlop, E. Gawiser, D. Lutz, P. van der Werf and A. Weiß.

The clustering of submillimeter galaxies (in red) in the Extended Chandra Deep Field-South was measured to determine that they eventually evolve into extremely massive galaxies. Credit: ESO, APEX (MPIfR/ESO/OSO), A. Weiss et al., NASA Spitzer Science Center

New paper: Intensity Mapping of the [CII] Fine Structure Line during the Epoch of Reionization

Intensity Mapping of the [CII] Fine Structure Line during the Epoch of Reionization

Yan Gong, Asantha Cooray, Marta Silva, Mario G. Santos, James Bock, Matt Bradford, Michael Zemcov, arXiv: 1107.3553

The atomic CII fine-structure line is one of the brightest lines in a typical star-forming galaxy
spectrum with a luminosity ~ 0.1% to 1% of the bolometric luminosity. It is potentially a reliable tracer of the dense gas  distribution at high redshifts and could
provide an additional probe to the era of reionization. By taking into account of the spontaneous, stimulated and collisional emission of the CII line, we calculate the spin temperature and the mean intensity as a function of the redshift. When averaged over a cosmologically large volume,  we find that the CII emission from ionized carbon in
individual galaxies is larger than the signal generated by carbon in the intergalactic medium (IGM). Assuming that the CII luminosity is proportional to the carbon mass in dark matter halos, we also compute the power spectrum of the CII line intensity at various redshifts.
In order to avoid the contamination from CO rotational lines at low redshift when targeting a CII survey at high redshifts, we propose the cross-correlation of CII and 21-cm line emission
from high redshifts. To explore the detectability of the CII signal from reionization, we also evaluate the expected errors on the CII power spectrum and CII-21 cm cross power spectrum based on the design of the future milimeter surveys. We note that the CII-21 cm cross power spectrum contains interesting features that captures physics during reionization, including the
ionized bubble sizes and the mean ionization fraction, which are challenging to measure from 21-cm data alone. We propose an instrumental concept for the reionization CII experiment  targeting the frequency range of ~ 200 to 300 GHz with 1, 3 and 10 meter apertures and a bolometric spectrometer array with 64 independent spectral pixels with about 20,000 bolometers.

The clustering, shot-noise and total power spectrum of CII emission line at z=6, z=7 and z=8. The red solid, dashed and dotted lines denote the CII total, clustering and shot-noise power spectrum  espectively. The  clustering power spectrum is estimated from the simulation with only the hot gas contributing to the CII luminosity. The green dashed lines are the 1 sigma error of the CII power spectrum. The error bars and noise power spectrum (red long-dashed line) is estimated with 10m aperture dish for CII line. The magenta long dashed line is derived from the CII luminosity estimated by Visbal & Loeb 2010. The blue dash-dotted line is estimated via the relation L_CII/L_ CO(1-0) ~ 10^4.

Letter to Editor in Nature (on line publication Feb 16, 2011; print Feb 24, 2011)

A paper led by the Cooray group for the Herschel-SPIRE Instrument Team now appearing in Nature:

Submillimetre galaxies reside in dark matter haloes with masses greater than 3 × 1011 solar masses

Alexandre Amblard, Asantha Cooray, Paolo Serra (all of UC Irvine) et al.

Link to Nature online article || Paper PDF from Nature

Nature abstract:

The extragalactic background light at far-infrared wavelengths123 comes from optically faint, dusty, star-forming galaxies in the Universe with star formation rates of a few hundred solar masses per year4. These faint, submillimetre galaxies are challenging to study individually because of the relatively poor spatial resolution of far-infrared telescopes56. Instead, their average properties can be studied using statistics such as the angular power spectrum of the background intensity variations78910. A previous attempt11at measuring this power spectrum resulted in the suggestion that the clustering amplitude is below the level computed with a simple ansatz based on a halo model12. Here we report excess clustering over the linear prediction at arcminute angular scales in the power spectrum of brightness fluctuations at 250, 350 and 500 μm. From this excess, we find that submillimetre galaxies are located in dark matter haloes with a minimum mass, Mmin, such that log10[Mmin/M] =  at 350 μm, where M is the solar mass. This minimum dark matter halo mass corresponds to the most efficient mass scale for star formation in the Universe13, and is lower than that predicted by semi-analytical models for galaxy formation14.

This false-colour image shows a patch of the sky known as the ‘Lockman Hole’, as observed by the SPIRE instrument on board Herschel. Credits: ESA & SPIRE consortium & HerMES consortium

The image on the left is of the ‘Lockman Hole’, a field that was observed by the SPIRE instrument and is a region of key interest to observe galaxies in the distant universe, since it has little foreground contamination.

The false-colour image is filled with many dots that represent an entire galaxy. Colours on the image are blue, green, and red and it represents the three far-IR wavelengths of the SPIRE instrument: 250, 350, and 500 microns. Dots that are shown as white have equal intensity in all three wavelengths and are the ones with high star formation rates.

Distribution of dark matter, obtained from a numerical simulation, at a redshift z~2; showing the continuous distribution (first frame), a simplified view of the complex network of dark matter structure (second frame) and the most massive dark matter halos - shown in yellow (third frame). Credit: From Amblard, Cooray, Serra et al., Nature, 2011

The work is subject to several public news stories and articles.

NASA Press release: Herschel Measures Dark Matter for Star-Forming Galaxies

ESA Press release: Herschel finds less dark matter but more stars

ESA Science and Technology Article: Herschel quantifies the dark matter threshold for starburst galaxies

New Paper: Cosmic Magnification of Herschel Sources Detected!

HerMES: detection of cosmic magnification of sub-mm galaxies using angular cross-correlation⋆

L. Wang, A. Cooray, D. Farrah, et al. MNRAS in press

Cosmic magnification is due to the weak gravitational lensing of sources in the dis- tant Universe by foreground large-scale structure leading to coherent changes in the observed number density of the background sources. Depending on the slope of the background source number counts, cosmic magnification causes a correlation between the background and foreground galaxies, which is unexpected in the absence of lensing if the two populations are spatially disjoint. Previous attempts using submillimetre (sub-mm) sources have been hampered by small number statistics. The large num- ber of sources detected in the Herschel Multi-tiered Extra-galactic Survey (HerMES) Lockman-SWIRE field enables us to carry out the first robust study of the cross- correlation between sub-mm sources and sources at lower redshifts. Using ancillary data we compile two low-redshift samples from SDSS and SWIRE with ⟨z⟩ ∼ 0.2 and 0.4, respectively, and cross-correlate with two sub-mm samples based on flux density and colour criteria, selecting galaxies preferentially at z ∼ 2. We detect cross- correlation on angular scales between ∼ 1 and 50 arcmin and find clear evidence that this is primarily due to cosmic magnification. A small, but non-negligible signal from intrinsic clustering is likely to be present due to the tails of the redshift distribution of the sub-mm sources overlapping with those of the foreground samples.


A new paper from our group now appears in the Astrophysical Journal Letters discussing the use of molecular (mainly rotational lines of carbon-monoxide) and atomic fine-structure lines (CII line associated with carbon) to probe the era of reionization especially at redshifts around 7 or 8.



The abstract is:

We propose observations of the molecular gas distribution during the era of reionization. At z ∼ 6 to 8, 12 CO(J = 1 − 0) line intensity results in a mean brightness temperature of about 0.5 μK with rms fluctuations of 0.1 μK at 1 to 10 Mpc spatial scales, corresponding to 30 arcminute angular scales. This intensity fluctuations can be mapped with an interferometer, similar to existing and planned 21-cm background experiments, but operating at ∼ 12 to 17 GHz. We discuss the feasibility of detecting the cross-correlation between HI and CO molecular gas since such a cross-correlation has the advantage that it will be independent of systematics and most foregrounds in each of the 21-cm and CO(1 − 0) line experiments. Additional instruments tuned to higher-order transitions of the CO molecule or an instrument operating with high spectral resolution at mm- wavelengths targeting 158 μm CII could further improve the reionization studies with molecular gas. The combined 21-cm and CO line observations has the potential to establish the relative distribution of gas in the inter-galactic medium and molecular gas that are clumped in individual first-light galaxies that are closely connected to the formation of massive stars in these galaxies.

the dimensionless cross power spectrum and shot-noise power spectrum for CO line and 21 cm emission at z = 7.

The dimensionless cross power spectrum and shot-noise power spectrum for CO line and
21 cm emission at z = 7. The blue solid line is the error from LOFAR. The 68.3% CL (1σ ) is shown in red thin lines. The long-dashed magenta lines in the middle
and right panels are the results from the simulation of 21 cm in Santos et al. (2010) for comparison.

January 2011 American Astronomical Society Meeting Presentations

Our group will be doing 6 poster presentations at the January 2011 AAS meeting in Seattle, WA. We make available pdf copies of these posters below. In addition to posters, Prof. Cooray has organized a special session at the AAS on Wed Jan 12th from 2 to 3:30 pm on the topic “Joint Astrophysics and Planetary Science Studies from the Outer Solar System”. The session will discuss astrophysics instruments on NASA planetary science missions with scientific goals involving diffuse background studies such as the extragalactic background light and the dust at KBO distances and the possibility for micro-lensing and extra-solar planetary transit observations.

Group posters

Cooray et al. (SPIRE Instrument Science Team HerMES)   Tracing the Sources of the Cosmic Far-Infrared Background with Unresolved Fluctuations

Smidt et al. A lensing measurement of the dark matter power spectrum with WMAP CMB maps

Kim et al. (Herschel-ATLAS) Spitzer-IRAC counterparts to Herschel-ATLAS sources using the likelihood ratio test

Mitchell-Wynne et al. (SPIRE Instrument Team HerMES) Redshift distribution of SPIRE sources using the cross-correlation with Spitzer IRAC sources

Khostovan et al. (Herschel-ATLAS team) Spitzer detection of lensed sub-mm galaxies in Herschel-ATLAS

Frazer et al. (CIBER team) Cosmic Infrared Background Experiment

Postdoctoral Positions Available

We have two postdoctoral positions for three years each available from summer/fall 2011. The positions are related to Herschel surveys, HerMES and ATLAS, and HST MCT CANDELS. They require experience with any of wide-field cosmology and analysis of large datasets for large-scale structure measurements, Herschel, Spitzer, and ground-based follow-up studies of sub-mm and IR-bright galaxies, gravitational lensing observations and lens modeling, and optical and multi-wavelength ground-based studies of high-redshift galaxies.

Please apply for these positions as part of the general AAS Job ad. Applications are due on or before Dec 31st, 2010.