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Register a new userMorphologies and Spectral Energy Distributions of Extremely Red Galaxies in the GOODS-South Field
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Leonidas A. Moustakas
Publication date
2003
fields
Physics
and research's language is
English
Authors
Leonidas A. Moustakas
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Using U- through Ks-band imaging data in the GOODS-South field, we construct a large, complete sample of 275 ``extremely red objects (EROs; K_s<22.0, R-K_s>3.35; AB), all with deep HST/ACS imaging in B_435, V_606, i_775, and z_850, and well-calibrated photometric redshifts. Quantitative concentration and asymmetry measurements fail to separate EROs into distinct morphological classes. We therefore visually classify the morphologies of all EROs into four broad types: ``Early (elliptical-like), ``Late (disk galaxies), ``Irregular and ``Other (chain galaxies and low surface brightness galaxies), and calculate their relative fractions and comoving space densities. For a broad range of limiting magnitudes and color thresholds, the relative number of early-type EROs is approximately constant at 33-44%, and the comoving space densities of Early- and Late-type EROs are comparable. Mean rest-frame spectral energy distributions (SEDs) at wavelengths between 0.1 and 1.2 um are constructed for all EROs. The SEDs are extremely similar in their range of shapes, independent of morphological type. The implication is that any differences between the broad-band SEDs of Early-type EROs and the other types are relatively subtle, and there is no robust way of photometrically distinguishing between different morphological types with usual optical/near-infrared photometry.
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We present a new cataloge of EROs from the Groth strip and study the relation between their morphology and mass. We find 102 EROs (F814W-K=>4, K<=21.0), over a survey area of 155 arcmin^2. The photometric data include U,B,F606W,F814W,J,K bands. Morphologies are based on a by eye classification and we distinguish between 3 basic classes: compact objects, targets with a disc and/or a bulge component and irregular or merger candidates. The majority of our targets has either a very compact morphology (33+-6%), or show more or less distinct disc components (41+-6%). 14+-4% are merger or irregulars and 7 objects could not be classified. We also study the dependence of structural parameters on morphological appearance. EROs that are either compact or show a distinct bulge component have smaller median effective radii (1.22+-0.14 kpc and 3.31+-0.53 kpc) than disc dominated (5.50+-0.51 kpc) or possible irregular galaxies or merger candidates (4.92+-0.14 kpc). The Sersic index changes from 2.30+-0.34 and 3.24+-0.55, to 1.03+-0.24 and 1.54+-0.40 respectively. Most the EROs in our sample have redshifts between z=1 and z=2; however, compact EROs in our sample are found at redshifts as low as z=0.4 and as high as z=2.8; the latter qualify as well as DRGs. Disc-like EROs are also found up to z=2.8; however those with a bulge-disc structure are only seen at z<1.5. For each of these EROs we determined the stellar mass and mean population age by fitting synthetic Bruzual (2007) spectra to the SED. Mass estimates were obtained by assuming an exponentially declining star formation rate. Total stellar masses are in the range 9.1<log(M/M_sun)<11.6. We cannot detect significant differences between the stellar mass distribution of the morphological classes. EROs with masses of log(M/M_sun)>11.0 dominantly show compact morphologies, but also include a significant number of sources with a disc morphology.
We have studied the spatial clustering of high redshift (z > 1) extremely red objects (EROs) as a function of photometric redshift in the GOODS Southern Field using public data. A remarkable overdensity of extremely red galaxies (I-Ks > 4) is found at an average photometric redshift z=1.10. Nine objects (six are EROs) within 50 arcsec of the brightest infrared galaxy in this overdensity present spectroscopic redshifts in the range 1.094 < z < 1.101 with a line-of-sight velocity dispersion of 433 km/s typical of an Abell richness class R=0 cluster. Other potential members of this cluster, designated as GCL J0332.2-2752, have been identified using photometric redshifts and the galaxy density profile studied as a function of radius. The mass of the cluster is preliminary estimated at M ~ 5-7 x 10^{13} M_{sun}. Using available Chandra data, we limit the rest-frame X-ray luminosity of the cluster to less than L_X = 7.3 x 10^{42} erg/s (0.5-2.0 keV). This low-mass, low L_X cluster at z > 1 shows the potential of EROs to trace clusters of galaxies at high redshift.
We present infrared (IR) to X-ray spectral energy distributions (SEDs) for 44 red AGN selected from the 2MASS survey on the basis of their red J-K$_S$ color (>2 mag) and later observed by Chandra. In comparison with optically-, radio-, and X-ray selected AGN, their median SEDs are red in the optical and near-IR with little/no blue bump. It thus seems that near-IR color selection isolates the reddest subset of AGN that can be classified optically. The shape of the SEDs is generally consistent with modest absorption by gas (in the X-ray) and dust (in the optical-IR). The levels of obscuration, estimated from X-rays, far-IR and our detailed optical/near-IR color modeling are all consistent implying N_H < few*10^{22} cm^{-2}. We present SED models that show how the AGN optical/near-IR colors change due to differing amounts of reddening, AGN to host galaxy ratio, redshift and scattered light emission and apply them to the sources in the sample. We find that the 2MASS AGN optical color, B-R, and to a lesser extent the near-IR color, J-K$_S$, are strongly affected by reddening, host galaxy emission, redshift, and in few, highly polarized objects, also by scattered AGN light. The obscuration/inclination of the AGN allows us to see weaker emission components which are generally swamped by the AGN.
We present a high quality multiwavelength (from 0.3 to 8.0 micron) catalog of the large and deep area in the GOODS Southern Field covered by the deep near-IR observations obtained with the ESO VLT. The catalog is entirely based on public data: in our analysis, we have included the F435W, F606W, F775W and F850LP ACS images, the JHKs VLT data, the Spitzer data provided by IRAC instrument (3.6, 4.5, 5.8 and 8.0 micron), and publicly available U-band data from the 2.2ESO and VLT-VIMOS. We describe in detail the procedures adopted to obtain this multiwavelength catalog. In particular, we developed a specific software for the accurate PSF-matching of space and ground-based images of different resolution and depth (ConvPhot), of which we analyse performances and limitations. We have included both z-selected, as well as Ks-selected objects, yielding a unique, self-consistent catalog. The largest fraction of the sample is 90% complete at z~26 or Ks~23.8 (AB scale). Finally, we cross-correlated our data with all the spectroscopic catalogs available to date, assigning a spectroscopic redshift to more than 1000 sources. The final catalog is made up of 14847 objects, at least 72 of which are known stars, 68 are AGNs, and 928 galaxies with spectroscopic redshift (668 galaxies with reliable redshift determination). We applied our photometric redshift code to this data set, and the comparison with the spectroscopic sample shows that the quality of the resulting photometric redshifts is excellent, with an average scatter of only 0.06. The full catalog, which we named GOODS-MUSIC (MUltiwavelength Southern Infrared Catalog), including the spectroscopic information, is made publicly available, together with the software specifically designed to this end.
We examine the evolution of the sizes and number densities of disk galaxies using the high resolution images obtained by the Great Observatories Origins Deep Survey (GOODS) with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). The multiwavelength (B,V,i,z) images allow us to classify galaxies based on their rest-frame B-band morphologies out to redshift z = 1.25. In order to minimize the effect of selection biases, we confine our analysis to galaxies which occupy the region of magnitude-size plane where the survey is almost 90% complete at all redshifts. The observed size distribution is consistent with a log-normal distribution as seen for the disk galaxies in the local Universe and does not show any significant evolution over the redshift range 0.25 < z < 1.25. We find that the number densities of disk galaxies remains fairly constant over this redshift range, although a modest evolution by a factor of four may be possible within the 2-sigma uncertainties.
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