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V. Smolčić,
E. Schinnerer,
M. Scodeggio,
P. Franzetti,
H. Aussel,
M. Bondi,
M. Brusa,
C. L. Carilli,
P. Capak,
S. Charlot, [......],
H. J. McCracken,
M. Obrić,
M. Salvato,
D. B. Sanders,
N. Scoville,
J. R. Trump, C. Tremonti,
L. Tasca,
C. J. Walcher,
and G. Zamorani
[show abstract]
[hide abstract]
ABSTRACT: We explore the properties of the submillijansky radio population at 20 cm by applying a newly developed optical color-based method to separate star-forming (SF) from active galactic nucleus (AGN) galaxies at intermediate redshifts (z 1.3). Although optical rest-frame colors are used, our separation method is shown to be efficient and not biased against dusty starburst galaxies. This classification method has been calibrated and tested on a local radio-selected optical sample. Given accurate multiband photometry and redshifts, it carries the potential to be generally applicable to any galaxy sample where SF and AGN galaxies are the two dominant populations. In order to quantify the properties of the submillijansky radio population, we have analyzed ~2,400 radio sources, detected at 20 cm in the VLA-COSMOS survey; 90% of these have submillijansky flux densities. We classify the objects into (1) star candidates, (2) quasi-stellar objects, (3) AGN, (4) SF, and (5) high-redshift (z > 1.3) galaxies. We find, for the composition of the submillijansky radio population, that SF galaxies are not the dominant population at submillijansky flux levels, as previously often assumed, but that they make up an approximately constant fraction of 30%-40% in the flux density range of ~50 μJy to 0.7 mJy. In summary, based on the entire VLA-COSMOS radio population at 20 cm, we find that the radio population at these flux densities is a mixture of roughly 30%-40% of SF and 50%-60% of AGN galaxies, with a minor contribution (~10%) of QSOs.
The Astrophysical Journal Supplement Series 12/2008; 177(1):14. · 13.46 Impact Factor
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M. Obrić,
Ž. Ivezić,
P. N. Best,
R. H. Lupton, C. Tremonti,
J. Brinchmann,
M. A. Agüeros,
G. R. Knapp,
J. E. Gunn,
C. M. Rockosi, [......],
M. Gaćeša,
V. Smolčić,
S. F. Anderson,
W. Voges,
M. Jurić,
R. J. Siverd,
W. Steinhardt,
A. S. Jagoda,
M. R. Blanton,
D. P. Schneider
[show abstract]
[hide abstract]
ABSTRACT: We discuss the panchromatic properties of 99 088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 ‘main’ spectroscopic sample (a flux-limited sample for 1360 deg2). These galaxies are positionally matched to sources detected by ROSAT, Galaxy Evolution Explorer (GALEX), two-Micron All-Sky Survey (2MASS), Infrared Astronomical Satellite (IRAS), Green Bank GB6 survey (GB6), Faint Images of the Radio Sky at Twenty-centimetres (FIRST), NRAO VLA Sky Survey (NVSS) and Westerbork Northern Sky Survey (WENSS). The matching fraction varies from <1 per cent for ROSAT and GB6 to ∼40 per cent for GALEX and 2MASS. In addition to its size, the advantages of this sample are well-controlled selection effects, faint flux limits and the wealth of measured parameters, including accurate X-ray to radio photometry, angular sizes and optical spectra. We find strong correlations between the detection fraction at other wavelengths and optical properties such as flux, colours and emission-line strengths. For example, ∼2/3 of SDSS ‘main’ galaxies classified as active galactic nucleus (AGN) using emission-line strengths are detected by 2MASS, while the corresponding fraction for star-forming galaxies (SFs) is only ∼1/10. Similarly, over 90 per cent of galaxies detected by IRAS display strong emission lines in their optical spectra, compared to ∼50 per cent for the whole SDSS sample. Using GALEX, SDSS and 2MASS data, we construct the ultraviolet–infrared (UV–IR) broad-band spectral energy distributions for various types of galaxies, and find that they form a nearly one-parameter family. For example, the SDSS u- and r-band data, supplemented with redshift, can be used to ‘predict’K-band magnitudes measured by 2MASS with an rms scatter of only 0.2 mag. When a dust content estimate determined from SDSS spectra with the aid of models is also utilized, this scatter decreases to 0.1 mag and can be fully accounted for by measurement uncertainties. We demonstrate that this interstellar dust content, inferred from optical SDSS spectra by Kauffmann et al., is indeed higher for galaxies detected by IRAS and that it can be used to ‘predict’ measured IRAS 60 μm flux density within a factor of 2 using only SDSS data. We also show that the position of a galaxy in the emission-line-based Baldwin–Phillips–Terlevich diagram is correlated with the optical light concentration index and u−r colour determined from the SDSS broad-band imaging data, and discuss changes in the morphology of this diagram induced by requiring detections at other wavelengths. Notably, we find that SDSS ‘main’ galaxies detected by GALEX include a non-negligible fraction (10–30 per cent) of AGNs, and hence do not represent a clean sample of starburst galaxies. We study the IR–radio correlation and find evidence that its slope may be different for AGN and SFs and related to the H/Hβ line-strength ratio.
Monthly Notices of the Royal Astronomical Society 08/2006; 370(4):1677 - 1698. · 4.90 Impact Factor
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V. Smolcic,
Z. Ivezic,
M. Gacesa,
K. Rakos,
K. Pavlovski,
S. Ilijic,
M. Obric,
R. H. Lupton,
D. Schlegel,
G. Kauffmann, C. Tremonti,
J. Brinchmann,
S. Charlot,
T. M. Heckman,
G. R. Knapp,
J. E. Gunn,
J. Brinkmann,
I. Csabai,
M. Fukugita,
J. Loveday
[show abstract]
[hide abstract]
ABSTRACT: We synthesize the rest-frame Stroemgren colors using SDSS spectra for 99,088 galaxies selected from Data Release 1. This narrow-band ~200 AA photometric system (uz, vz, bz, yz), first designed for the determination of effective temperature, metallicity and gravity of stars, measures the continuum spectral slope of galaxies in the rest-frame 3200-5800 AA wavelength range. Galaxies form a remarkably narrow locus (~0.03 mag) in the resulting color-color diagram. The Bruzual & Charlot population synthesis models suggest that the position of a galaxy along this locus is controlled by a degenerate combination of metallicity and age of the dominant stellar population. Galaxy distribution along the locus is bimodal, with the local minimum corresponding to an ~1 Gyr old single stellar population. The position perpendicular to the locus is independent of metallicity and age, and reflects the galaxy's dust content, as implied by both the models and the statistics of IRAS detections. A comparison of this locus with the galaxy locus in the H_delta-D_n(4000) diagram, utilized by Kauffmann et al. (2003) to estimate stellar masses, reveals a tight correlation, although the two analyzed spectral ranges barely overlap. Overall, the galaxy spectral energy distribution in the entire UV to near-IR range can be described as a single-parameter family with an accuracy of 0.1 mag, or better. This nearly one-dimensional distribution of galaxies in the multi-dimensional space of measured parameters strongly supports the conclusion of Yip et al. (2004), based on a principal component analysis, that SDSS galaxy spectra can be described by a small number of eigenspectra. Apparently, the contributions of stellar populations that dominate the optical emission from galaxies are combined in a simple and well-defined way.
07/2006;
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M. Obric,
Z. Ivezic,
G. Kauffmann,
R. H. Lupton, C. Tremonti,
J. Brinchmann,
S. Charlot,
G. R. Knapp,
J. E. Gunn,
C. M. Rockosi,
D. Schlegel,
M. A. Strauss,
M. Gacesa,
V. Smolcic,
S Anderson,
W. Voges,
M. R. Blanton,
D. Eisenstein
[show abstract]
[hide abstract]
ABSTRACT: We summarize the detection rates at wavelengths other than optical for \~99,000 galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 1 ``main'' spectroscopic sample. The analysis is based on positional cross-correlation with source catalogs from ROSAT, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS surveys. We find that the rest-frame UV-IR broad-band galaxy SEDs form a remarkably uniform, nearly one parameter, family. As an example, the SDSS u and r band data, supplemented with redshift, can be used to predict K band magnitudes measured by 2MASS with an rms scatter of only 0.2 mag; when measurement uncertainties are taken into account, the astrophysical scatter appears not larger than ~0.1 mag. Comment: 2 pages, 1 figure. To appear in "The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", Proc. IAU 222 (Gramado, Brazil), eds. Th. Storchi Bergmann, L.C. Ho, H.R. Schmitt
04/2004;
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[show abstract]
[hide abstract]
ABSTRACT: (modified) We present a comprehensive study of the physical properties of \~10^5 galaxies with measurable star formation in the SDSS. By comparing physical information extracted from the emission lines with continuum properties, we build up a picture of the nature of star-forming galaxies at z<0.2. We take out essentially all aperture bias using resolved imaging, allowing an accurate estimate of the total SFRs in galaxies. We determine the SFR density to be 1.915^{+0.02}_{-0.01}(rand.)^{+0.14}_{-0.42} (sys.) h70 10^{-2} Msun/yr/Mpc^3 at z=0.1 (for a Kroupa IMF) and we study the distribution of star formation as a function of various physical parameters. The majority of the star formation in the low redshift universe takes place in moderately massive galaxies (10^10-10^11 Msun), typically in HSB disk galaxies. Roughly 15% of all star formation takes place in galaxies that show some sign of an active nucleus. About 20% occurs in starburst galaxies. We show that the present to past-average star formation rate, the Scalo b-parameter; is almost constant over almost three orders of magnitude in mass, declining only at M*>10^10 Msun. The volume averaged b parameter is 0.408^{+0.005}_{-0.002} (rand).^{+0.029}_{-0.090} (sys.) h70^{-1}. We use this value constrain the star formation history of the universe. In agreement with other work we find a correlation between $b$ and morphological type, as well as a tight correlation between the 4000AA break (D4000) and b. We discuss how D4000 can be used to estimate b parameters for high redshift galaxies. Comment: Accepted for MNRAS. Replaced with accepted version. A section on comparison with other methods of SFR estimation added and various updates have been made. The main results are almost unchanged
11/2003;
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[show abstract]
[hide abstract]
ABSTRACT: We discuss the optical and radio properties of 30,000 FIRST sources positionally associated with an SDSS source in 1230 deg$^2$ of sky. The majority (83%) of the FIRST sources identified with an SDSS source brighter than r=21 are optically resolved. We estimate an upper limit of 5% for the fraction of quasars with broad-band optical colors indistinguishable from those of stars. The distribution of quasars in the radio flux -- optical flux plane supports the existence of the "quasar radio-dichotomy"; 8% of all quasars with i<18.5 are radio-loud and this fraction seems independent of redshift and optical luminosity. The radio-loud quasars have a redder median color by 0.08 mag, and a 3 times larger fraction of objects with red colors. FIRST galaxies represent 5% of all SDSS galaxies with r<17.5, and 1% for r<20, and are dominated by red galaxies. Magnitude and redshift limited samples show that radio galaxies have a different optical luminosity distribution than non-radio galaxies selected by the same criteria; when galaxies are further separated by their colors, this result remains valid for both blue and red galaxies. The distributions of radio-to-optical flux ratio are similar for blue and red galaxies in redshift-limited samples; this similarity implies that the difference in their luminosity functions, and resulting selection effects, are the dominant cause for the preponderance of red radio galaxies in flux-limited samples. We confirm that the AGN-to-starburst galaxy number ratio increases with radio flux, and find that radio emission from AGNs is more concentrated than radio emission from starburst galaxies (abridged). Comment: submitted to AJ, color gif figures, PS figures available from ivezic@astro.princeton.edu
02/2002;
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G. Kauffmann,
T. M. Heckman, C. Tremonti,
J. Brinchmann,
S. Charlot,
S. D. M. White,
S. E. Ridway,
J. Brinkmann,
M. Fukugita,
P. B. Hall,
Z. Ivezic,
G. T. Richards,
D. P. Schneider
Monthly Notices of the Royal Astronomical Society, v.346, 1055-1077 (2003).
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V. Smolcic,
Z. Ivezic,
M. Gacesa,
K. Rakos,
K. Pavlovski,
S. Ilijic,
M. Obric,
R. H. Lupton,
D. Schlegel,
G. Kauffmann, C. Tremonti,
J. Brinchmann,
S. Charlot,
T. M. Heckman,
G. R. Knapp,
J. E. Gunn,
J. Brinkmann,
I. Csabai,
M. Fukugita,
J. Loveday
[show abstract]
[hide abstract]
ABSTRACT: We discuss the colours of 99088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 `main' spectroscopic sample (a flux-limited sample, rPet < 17.77, for 1360 deg2) in the rest-frame Strömgren system (uz, vz, bz, yz). This narrow-band (~200 Å) photometric system, first designed for the determination of effective temperature, metallicity and gravity of stars, measures the continuum spectral slope of galaxies in the rest-frame 3200-5800 Å wavelength range. We synthesize rest-frame Strömgren magnitudes from SDSS spectra, and find that galaxies form a remarkably narrow locus (~0.03 mag) in the resulting colour-colour diagram. Using the Bruzual & Charlot population-synthesis models, we demonstrate that the position of a galaxy along this locus is controlled by metallicity and age of the dominant stellar population. The distribution of galaxies along the locus is bimodal, with the local minimum corresponding to an ~1-Gyr-old single stellar population. The position of a galaxy perpendicular to the locus is independent of metallicity and age, and reflects the galaxy's dust content, as implied by both the models and the statistics of IRAS detections. Comparison of the galaxy locus in the rest-frame Strömgren colour-colour diagram with the galaxy locus in the HdeltaA-Dn(4000) diagram, utilized by Kauffmann et al. to estimate stellar masses, reveals a tight correlation, although the two analysed spectral ranges barely overlap. Furthermore, the rest-frame r - i colour (5500-8500 Å wavelength range) can be `predicted' with an rms of 0.05 mag using the rest-frame Strömgren colours. Overall, the galaxy spectral energy distribution in the entire ultraviolet to near-infrared range can be described as a single-parameter family with an accuracy of 0.1 mag, or better. This nearly one-dimensional distribution of galaxies in the multidimensional space of measured parameters strongly supports the conclusion of Yip et al., based on a principal component analysis, that SDSS galaxy spectra can be described by a small number of eigenspectra. Furthermore, the rest-frame Strömgren colours correlate tightly with the classification scheme proposed by Yip et al. based on the first three eigenspectra. Apparently, the contributions of stellar populations that dominate the optical emission from galaxies are combined in a simple and well-defined way. We also find a remarkably tight correlation between the rest-frame Strömgren colours of emission-line galaxies and their position in the Baldwin-Phillips-Terlevich diagram. These correlations between colours and various spectroscopic diagnostic parameters support earlier suggestions that rest-frame Strömgren photometry offers an efficient tool to study faint cluster galaxies and low surface brightness objects without performing time-consuming spectral observations.
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C. W. Yip,
A. J. Connolly,
D. E. Vanden Berk,
R. Scranton,
S. Krughoff,
A. S. Szalay,
L. Dobos, C. Tremonti,
M. Taghizadeh-Popp,
T. Budavári,
I. Csabai,
R. F. G. Wyse,
Z. Ivezic
[show abstract]
[hide abstract]
ABSTRACT: Under the unified model for active galactic nuclei (AGNs), narrow-line (Type 2) AGNs are, in fact, broad-line (Type 1) AGNs but each with a heavily obscured accretion disk. We would therefore expect the optical continuum emission from Type 2 AGNs to be composed mainly of stellar light and nonvariable on the timescales of months to years. In this work we probe the spectroscopic variability of galaxies and narrow-line AGNs using the multiepoch data in the Sloan Digital Sky Survey Data Release 6. The sample contains 18,435 sources for which there exist pairs of spectroscopic observations (with a maximum separation in time of ~700 days) covering a wavelength range of 3900-8900 Ãâ¦. To obtain a reliable repeatability measurement between each spectral pair, we consider a number of techniques for spectrophotometric calibration resulting in an improved spectrophotometric calibration of a factor of 2. From these data we find no obvious continuum and emission-line variability in the narrow-line AGNs on averageââ¬âthe spectroscopic variability of the continuum is 0.07 ñ 0.26 mag in the g band and, for the emission-line ratios log10([N II]/Hñ) and log10([O III]/Hò), the variability is 0.02 ñ 0.03 dex and 0.06 ñ 0.08 dex, respectively. From the continuum variability measurement we set an upper limit on the ratio between the flux of the varying spectral component, presumably related to AGN activities, and that of the host galaxy to be ~30%. We provide the corresponding upper limits for other spectral classes, including those from the BPT diagram, eClass galaxy classification, stars, and quasars.
The Astronomical Journal, v.137, 5120-5133 (2009).
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M. Obric,
Z. Ivezic,
P. N. Best,
R. H. Lupton, C. Tremonti,
J. Brinchmann,
M. A. Agüros,
G. R. Knapp,
J. E. Gunn,
C. M. Rockosi, [......],
M. Gacesa,
V. Smolcic,
S. F. Anderson,
W. Voges,
M. Juric,
R. J. Siverd,
W. Steinhardt,
A. S. Jagoda,
M. R. Blanton,
D. P. Schneider
Monthly Notices of the Royal Astronomical Society, v.370, 1677-1698 (2006).
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V. Smolčić,
Z. Ivezić,
M. Gaćeša,
K. Rakos,
K. Pavlovski,
S. Ilijić,
M. Obrić,
R. H. Lupton,
D. Schlegel,
G. Kauffmann, C. Tremonti,
J. Brinchmann,
S. Charlot,
T. M. Heckman,
G. R. Knapp,
J. E. Gunn,
J. Brinkmann,
I. Csabai,
M. Fukugita,
J. Loveday
Monthly Notices of the Royal Astronomical Society, v.371, 121-137 (2006).
