The Spitzer View of the Extragalactic Universe Soifer, Baruch T; Helou, George; Werner, Michael
Annual review of astronomy and astrophysics,
01/2008, Letnik:
46, Številka:
1
Journal Article
Recenzirano
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The Spitzer Space Telescope was launched in August 2003. Scientists from around the world have applied its orders-of-magnitude gain in imaging and spectroscopic capability to a wide array of topics ...in extragalactic research. Spitzer studies have found massive galaxies at redshifts greater than 6, resolved the cosmic background at 200 μm > λ > 20 μm into the dusty infrared-luminous galaxies that comprise it, directly detected dust-enshrouded star formation, and measured the star formation history of the universe to z > 3. In this review we examine a small fraction of the extragalactic studies from Spitzer that have been conducted in its first three years of operations.
One possible way for spiral galaxies to internally evolve would be for gas to flow to the center and form stars in a central disk (pseudo-bulge). If the inflow rate is faster than the rate of star ...formation, a central concentration of gas will form. In this paper we present radial profiles of stellar and 8 km emission from polycyclic aromatic hydrocarbons (PAHs) for 11 spiral galaxies to investigate whether the interstellar medium in these galaxies contains a central concentration above that expected from the exponential disk. In general, we find that the two-dimensional CO and PAH emission morphologies are similar, and that they exhibit similar radial profiles. We find that in 6 of the 11 galaxies there is a central excess in the 8 km and CO emission above the inward extrapolation of an exponential disk. In particular, all four barred galaxies in the sample have strong central excesses in both 8 km and CO emission. These correlations suggest that the excess seen in the CO profiles is, in general, not simply due to a radial increase in the CO emissivity. In the inner disk, the ratio of the stellar to the 8 km radial surface brightness is similar for 9 of the 11 galaxies, suggesting a physical connection between the average stellar surface brightness and the average gas surface brightness at a given radius. We also find that the ratio of the CO to 8 km PAH surface brightness is consistent over the sample, implying that the 8 km PAH surface brightness can be used as an approximate tracer of the interstellar medium.
We present rest-frame 15 and 24 Delta *mm luminosity functions (LFs) and the corresponding star-forming LFs at z < 0.3 derived from the 5MUSES sample. Spectroscopic redshifts have been obtained for ...~98% of the objects and the median redshift is ~0.12. The 5-35 Delta *mm Infrared Spectrograph spectra allow us to estimate accurately the luminosities and build the LFs. Using a combination of starburst and quasar templates, we quantify the star formation (SF) and active galactic nucleus (AGN) contributions in the mid-IR spectral energy distribution. We then compute the SF LFs at 15 and 24 Delta *mm, and compare with the total 15 and 24 Delta *mm LFs. When we remove the contribution of AGNs, the bright end of the LF exhibits a strong decline, consistent with the exponential cutoff of a Schechter function. Integrating the differential LF, we find that the fractional contribution by SF to the energy density is 58% at 15 Delta *mm and 78% at 24 Delta *mm, while it goes up to ~86% when we extrapolate our mid-IR results to the total IR luminosity density. We confirm that the AGNs play more important roles energetically at high luminosities. Finally, we compare our results with work at z ~ 0.7 and confirm that evolution on both luminosity and density is required to explain the difference in the LFs at different redshifts.
We present a catalog of the 1525 most optically luminous galaxies from the Sloan Digital Sky Survey with r-band luminosity Lr > 8L* and redshift z < 0.3, including 84 super spirals, 15 super ...lenticulars, 14 super post-merger galaxies, and 1400 giant ellipticals. With mass in stars of 1011.3-1012M , super spirals and lenticulars are the most massive disk galaxies currently known. The specific star formation rates of super spirals place them on or below the star-forming main sequence. They must have formed stars at a high rate throughout their history in order to grow their massive, gigantic stellar disks and maintain their blue u − r integrated colors. Their disks are red on the inside and blue on the outside, consistent with inside-out growth. They tend to have small bulge-to-total (B/T) r-band luminosity ratios, characteristic of disk building via minor mergers and cold accretion. A large percentage of super disk galaxies (41%) have double nuclei, double disks, or other signatures of ongoing mergers. Most (72%) are found in moderate- to low-density environments, while the rest are found at the outskirts of clusters. It is likely that super spirals survive in these environments because they continue to accrete cold gas and experience only minor mergers at late times, by virtue of their enormous masses and angular momenta. We suggest that super post-mergers are the product of super spiral major mergers and may be the precursors of some giant elliptical galaxies found in low-density environments. We present two new gravitational lens candidates in an appendix.
Far-infrared line and continuum fluxes are presented for a sample of 227 galaxies observed with the Long Wavelength Spectrometer on the Infrared Space Observatory. The galaxy sample includes normal ...star-forming systems, starbursts, and active galactic nuclei covering a wide range of colors and morphologies. The data set spans some 1300 line fluxes, 600 line upper limits, and 800 continuum fluxes. Several fine-structure emission lines are detected that arise in either photodissociation or H ii regions: O iii 52 mum, N iii 57 mum, O i 63 mum, O iii 88 mum, N ii 122 mum, O i 145 mum, and C ii 158 mum. Molecular lines such as OH at 53, 79, 84, 119, and 163 mum, and H sub( 2)O at 58, 66, 75, 101, and 108 mum are also detected in some galaxies. In addition to those lines emitted by the target galaxies, serendipitous detections of Milky Way C ii 158 mum and an unidentified line near 74 mum in NGC 1068 are also reported. Finally, continuum fluxes at 52, 57, 63, 88, 122, 145, 158, and 170 mum are derived for a subset of galaxies in which the far-infrared emission is contained within the image75 super(image ) ISO LWS beam. The statistics of this large database of continuum and line fluxes, including trends in line ratios with the far-infrared color and infrared-to-optical ratio, are explored.
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