arXiv subjects

Frank Masci

Publications and source records attributed to Frank Masci.

43 records · Page 3Linked to original sources

arXiv2007

Galaxy Counts at 24 Microns in the SWIRE Fields

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.

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arXiv2005

Large Scale Structure at 24 Microns in the SWIRE Survey

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, $w_{2}(θ)=A(θ/deg)^{1-γ}$, we find [A,γ] = [(5.43\pm0.20)\times10^{-4},2.01\pm0.02] for the full sample (1-sigma errors throughout). We have inverted Limber's equation and estimated a spatial correlation length of $r_{0}=3.32\pm0.19 h^{-1}$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.

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arXiv2004

The First Measurements of Galaxy Clustering from IRAC Data of the Spitzer First Look Survey

We present the first results of the angular auto-correlation function of the galaxies detected by the Infrared Array Camera (IRAC) instrument in the First Look Survey (FLS) of the Spitzer Space Telescope. We detect significant signals of galaxy clustering within the survey area. The angular auto-correlation function of the galaxies detected in each of the four IRAC instrument channels is consistent with a power-law form $w(θ)=Aθ^{1-γ}$ out to $θ= 0.2\arcdeg$, with the slope ranging from $γ= 1.5$ to 1.8. We estimate the correlation amplitudes $A$ to be $2.95 \times 10^{-3}$, $2.03 \times 10^{-3}$, $4.53 \times 10^{-3}$, and $2.34 \times 10^{-3}$ at $θ=1\arcdeg$ for galaxies detected in the IRAC 3.6$μ$m, 4.5$μ$m, 5.8$μ$m, and 8.0$μ$m instrument channels, respectively. We compare our measurements at 3.6$μ$m with the previous K-band measurements, and discuss the implications of these results.

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arXiv2004

First Insights into the SWIRE Galaxy Populations

We characterize the SWIRE galaxy populations in the SWIRE validation field within the Lockman Hole, based on the 3.6-24$μ$ Spitzer data and deep U,g',r',r' optical imaging within an area ~1/3 sq. deg for ~16,000 Spitzer-SWIRE sources. The entire SWIRE survey will discover over 2.3 million galaxies at 3.6$μ$m and almost 350,000 at 24$μ$m; ~70,000 of these will be 5-band 3.6-24$μ$ detections. The colors cover a broad range, generally well represented by redshifted spectral energy distributions of known galaxy populations, however significant samples of unusually blue objects in the [3.6-4.5]$μ$m color are found, as well as many objects very red in the 3.6-24$μ$m mid-IR. Nine of these are investigated and are interpreted as star-forming systems, starbursts and AGN from z=0.37 to 2.8, with luminosities from L$_{IR}$=10$^{10.3}$ to 10$^{13.7}$ L$_{\odot}$

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arXiv2003

SWIRE: The SIRTF Wide-area InfraRed Extragalactic Survey

The SIRTF Wide-area InfraRed Extragalactic survey (SWIRE), the largest SIRTF Legacy program, is a wide-area, imaging survey to trace the evolution of dusty, star-forming galaxies, evolved stellar populations, and AGN as a function of environment, from redshifts z~3 to the current epoch. SWIRE will survey 7 high-latitude fields, totaling 60 - 65 sq. deg. in all 7 SIRTF bands: IRAC 3.6, 4.5, 5.6, 8 microns and MIPS 24, 70, 160 microns. The Legacy Extragalactic Catalog may contain in excess of 2 million IR-selected galaxies, dominated by (1) ~150,000 luminous infrared galaxies (LIRGs: L{FIR}>10^11 L_sun), ~7000 of these with z>2; (2) 1 million early-type galaxies, ~10,000 with z>2; and (3) \~20,000 classical AGN, plus significantly more dust-obscured QSO/AGN among the LIRGs. SWIRE will provide an unprecedented view of the evolution of galaxies, structure, and AGN. The key scientific goals of SWIRE are: (1) to determine the evolution of actively star-forming and passively evolving galaxies in order to understand the history of galaxy formation in the context of cosmic structure formation; (2) to determine the evolution of the spatial distribution and clustering of evolved galaxies, starbursts and AGN in the key redshift range, 0.5<z<3, over which much of cosmic evolution has occurred; (3) to determine the evolutionary relationship between ``normal galaxies'' and AGN, and the contribution of AGN accretion energy vs stellar nucleosynthesis to the cosmic backgrounds. SWIRE's large area is important to create statistically significant population samples over enough volume cells that we can resolve the star formation history as a function of epoch and environment The large volume is also optimised for finding rare objects.

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arXiv2001

Models for Multiband IR Surveys

Empirical 'backward' galaxy evolution models for IR-bright galaxies are constrained using multiband IR surveys. A new Monte-Carlo algorithm is developed for this task. It exploits a large library of realistic Spectral Energy Distributions (SEDs) of 837 local IR galaxies (IRAS 25$μm$ selected) from the UV (1000Å) to the radio (20cm), including ISO-measured 3--13$μm$ unidentified broad features (UIBs). The basic assumption is that the local correlation between SEDs and Mid-Infrared (MIR) luminosities can be applied to earlier epochs of the Universe. Three populations of IR sources are considered in the evolution models. These include (1) starburst galaxies, (2) normal late-type galaxies, and (3) galaxies with AGN. A set of models so constructed are compared with data from the literature. Predictions for number counts, confusion limits, redshift distributions, and color-color diagrams are made for multiband surveys using the upcoming SIRTF satellite.

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arXiv1999

Cosmological Obscuration by Galactic Dust: Effects of Dust Evolution

We explore the effects of dust in cosmologically distributed intervening galaxies on the high redshift universe using a generalised model where dust content evolves with cosmic time. The absorbing galaxies are modelled as exponential disks which form coevally, maintain a constant space density and evolve in dust content at a rate that is uniform throughout. We find that the inclusion of moderate to moderately weak amounts of evolution consistent with other studies can reduce the mean observed $B$-band optical depth to redshifts $z \simgt 1$ by at least 60% relative to non-evolving models. Our predictions imply that intervening galactic dust is unlikely to bias the optical counts of quasars at high redshifts and their evolution in space density derived therefrom.

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