Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLarge Scale Structure at 24 Microns in the SWIRE Survey
84
0
0.0
(
0
)
Authors
Frank Masci
Ask ChatGPT about the research
No Arabic abstract
We present initial results of galaxy clustering at 24um by analyzing statistics of the projected galaxy distribution from counts-in-cells. This study focuses on the ELAIS-N1 SWIRE field. The sample covers ~5.9 square-degrees and contains 24,715 sources detected at 24um to a 5.6-sigma limit of 250 micro-Jy (in the lowest coverage regions). We have explored clustering as a function of 3.6 - 24um color and 24um flux density using angular-averaged two-point correlation functions derived from the variance of counts-in-cells on scales 0.05-0.7 degrees. Using a power-law parameterization, $w_{2}(theta)=A(theta/deg)^{1-gamma}$, we find [A,gamma] = [(5.43pm0.20)times10^{-4},2.01pm0.02] for the full sample (1-sigma errors throughout). We have inverted Limbers equation and estimated a spatial correlation length of $r_{0}=3.32pm0.19 h^{-1}$Mpc for the full sample, assuming stable clustering and a redshift model consistent with observed 24um counts. We also find that blue [f(24)/f(3.6)<=5.5] and red [f(24)/f(3.6)>=6.5] galaxies have the lowest and highest $r_{0}$ values respectively, implying that redder galaxies are more clustered (by a factor of ~3 on scales >0.2 degree). Overall, the clustering estimates are smaller than those derived from optical surveys, but in agreement with results from IRAS and ISO in the mid-infrared. This extends the notion to higher redshifts that infrared selected surveys show weaker clustering than optical surveys.
rate research
Read More
This paper presents galaxy source counts at 24 microns in the six Spitzer Wide-field InfraRed Extragalactic (SWIRE) fields. The source counts are compared to counts in other fields, and to model predictions that have been updated since the launch of Spitzer. This analysis confirms a very steep rise in the Euclidean-normalized differential number counts between 2 mJy and 0.3 mJy. Variations in the counts between fields show the effects of sample variance in the flux range 0.5-10 mJy, up to 100% larger than Poisson errors. Nonetheless, a shoulder in the normalized counts persists at around 3 mJy. The peak of the normalized counts at 0.3 mJy is higher and narrower than most models predict. In the ELAIS N1 field, the 24 micron data are combined with Spitzer-IRAC data and five-band optical imaging, and these bandmerged data are fit with photometric redshift templates. Above 1 mJy the counts are dominated by galaxies at z less than 0.3. By 300 microJy, about 25% are between z ~ 0.3-0.8, and a significant fraction are at z ~ 1.3-2. At low redshifts the counts are dominated by spirals, and starbursts rise in number density to outnumber the spirals contribution to the counts below 1 mJy.
We present the Spitzer MIPS 24 micron source counts in the Extragalactic First Look Survey main, verification and ELAIS-N1 fields. Spitzers increased sensitivity and efficiency in large areal coverage over previous infrared telescopes, coupled with the enhanced sensitivity of the 24 micron band to sources at intermediate redshift, dramatically improve the quality and statistics of number counts in the mid-infrared. The First Look Survey observations cover areas of, respectively, 4.4, 0.26 and 0.015 sq.deg. and reach 3-sigma depths of 0.11, 0.08 and 0.03 mJy. The extragalactic counts derived for each survey agree remarkably well. The counts can be fitted by a super-Euclidean power law of index alpha=-2.9 from 0.2 to 0.9 mJy, with a flattening of the counts at fluxes fainter than 0.2 mJy. Comparison with infrared galaxy evolution models reveals a peaks displacement in the 24 micron counts. This is probably due to the detection of a new population of galaxies with redshift between 1 and 2, previously unseen in the 15 micron deep counts.
The Large Scale Structure (LSS) in the galaxy distribution is investigated using the Sloan Digital Sky Survey Early Data Release (SDSS EDR). Using the Minimal Spanning Tree technique we have extracted sets of filaments, of wall-like structures, of galaxy groups, and of rich clusters from this unique sample. The physical properties of these structures were then measured and compared with the expectations from Zeldovich theory. The measured characteristics of galaxy walls were found to be consistent with those for a spatially flat $Lambda$CDM cosmological model with $Omega_mapprox$ 0.3 and $Omega_Lambda approx$ 0.7, and for Gaussian initial perturbations with a Harrison -- Zeldovich power spectrum. Furthermore, we found that the mass functions of groups and of unrelaxed structure elements generally fit well with the expectations from Zeldovich theory, although there was some discrepancy for lower mass groups which may be due to incompleteness in the selected sample of groups. We also note that both groups and rich clusters tend to prefer the environments of walls, which tend to be of higher density, rather than the environments of filaments, which tend to be of lower density. Finally, we note evidence of systematic differences in the properties of the LSS between the Northern Galactic Cap stripe and the Southern Galactic Cap stripe -- in particular, in the physical properties of the walls, their spatial distribution, and the relative numbers of clusters embedded in walls. Because the mean separation of walls is $approx$ 60 -- 70$h^{-1}$ Mpc, each stripe only intersects a few tens of walls. Thus, small number statistics and cosmic variance are the likely drivers of these systematic differences.
(Abridged) Studying continuum emission from interstellar dust is essential to locating and characterizing the highest density regions in the interstellar medium. In particular, the early stages of massive star formation remain poorly understood. Our goal is to produce a large-scale, systematic database of massive pre- and proto-stellar clumps in the Galaxy, to understand how and under what conditions star formation takes place. A well characterized sample of star-forming sites will deliver an evolutionary sequence and a mass function of high-mass, star-forming clumps. This systematic survey at submm wavelengths also represents a preparatory work for Herschel and ALMA. The APEX telescope is ideally located to observe the inner Milky Way. The Large APEX Bolometer Camera (LABOCA) is a 295-element bolometer array observing at 870 microns, with a beam size of 19. Taking advantage of its large field of view (11.4) and excellent sensitivity, we started an unbiased survey of the Galactic Plane, with a noise level of 50-70 mJy/beam: the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). As a first step, we covered 95 sq. deg. These data reveal 6000 compact sources brighter than 0.25 Jy, as well as extended structures, many of them filamentary. About two thirds of the compact sources have no bright infrared counterpart, and some of them are likely to correspond to the precursors of (high-mass) proto-stars or proto-clusters. Other compact sources harbor hot cores, compact HII regions or young embedded clusters. Assuming a typical distance of 5 kpc, most sources are clumps smaller than 1 pc with masses from a few 10 to a few 100 M_sun. In this introductory paper, we show preliminary results from these ongoing observations, and discuss the perspectives of the survey.
We have used the ROSAT All-Sky Survey around the North Ecliptic Pole to construct a complete sample of galaxy clusters. The deep and contiguous nature of the survey affords us the opportunity to examine large-scale structure in the Universe on scales of hundreds of megaparsecs. We have identified over 99% of the 446 X-ray sources in the survey area. The cluster sample consists of 65 objects with redshifts approaching unity. Surprisingly, some 20% of the clusters exists in a wall-like structure at z=0.088 spanning the entire 9 deg x 9 deg survey region. This is a very significant extension of both the membership and the spatial extent to a known supercluster in this location.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
