Color Separation of Galaxy Types in the Sloan Digital Sky Survey Imaging Data

Strateva, Iskra; Ivezić, Željko; Knapp, G. R.; Narayanan, Vijay K.; Strauss, Michael A.; Gunn, James E.; Lupton, Robert H.; Schlegel, David J.; Bahcall, Neta A.; Brinkmann, J.; Brunner, Róbert; Budavàri, Tamás; Csabai, István; Castander, F. J.; Doi, Mamoru; Fukugita, M.; Győry, Zsuzsanna; Hamabe, M.; Hennessy, G. S.; Ichikawa, Takashi; Kunszt, Péter Z.; Lamb, D. Q.; McKay, Timothy A.; Okamura, S.; Racusin, J. L.; Sekiguchi, M.; Schneider, Donald P.; Shimasaku, Kazuhiro; York, Donald G.

doi:10.1086/323301

Cited by 1,493 publications

(1,447 citation statements)

References 21 publications

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“…Nakamura et al 2003;Shen et al 2003) and a more relaxed selection at C r ≥ 2.6 (e.g. Strateva et al 2001;Kauffmann et al 2003;Bell et al 2003). Bernardi et al (2010) found that the second threshold of the concentration index corresponds to a mix of E+S0+Sa types, while the first mainly selects elliptical galaxies, removing the majority of Sa's, but also some Es and S0s.…”

Section: Spectro-photometric Diagnostic Diagramsmentioning

confidence: 99%

Spectro-photometric properties of the bulk of the radio-loud AGN population

Baldi¹,

Capetti²

2010

A&A

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In a previous paper we showed that the radio sources selected by combining large area radio and optical surveys, have a strong deficit of radio emission with respect to 3CR radio-galaxies matched in line emission luminosity. We argued that the prevalence of sources with luminous extended radio structures in high flux-limited samples is due to a selection bias. Sources with low radio power form the bulk of the radio-loud AGN population but are still virtually unexplored. We here analyze their photometric and spectroscopic properties. From the point of view of their emission lines, the majority of the sample are Low Excitation Galaxies (LEG), similar to the 3CR objects at the same level of line luminosity. The hosts of the LEG are red, massive (10.5 < ∼ log M * /M < ∼ 12) Early-Type Galaxies (ETG) with large black hole masses (7.7 < ∼ log M BH /M < ∼ 9), statistically indistinguishable from the hosts of low redshift 3CR/LEG sources. No genuine radio-loud LEG could be found associated with black holes with a mass substantially smaller than 10 8 M or with a late type host. The fraction of galaxies with signs of star formation (∼5%) is similar to what is found in both the quiescent ETG and 3CR/LEG hosts. We conclude that the deficit in radio emission cannot be ascribed to differences in the properties of their hosts. We argue that instead this could be due to a temporal evolution of the radio luminosity. A minority (∼10%) of the sample show rather different properties; these are associated with low black hole masses, with spiral galaxies, or with a high excitation spectrum. In general these outliers are the result of the contamination from Seyfert galaxies and from those where the radio emission is powered by star formation. For the objects with high excitation spectra there is no clear discontinuity in either the host or nuclear properties because they include radio-quiet as well as radio-loud AGN.

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Section: Spectro-photometric Diagnostic Diagramsmentioning

confidence: 99%

Spectro-photometric properties of the bulk of the radio-loud AGN population

Baldi¹,

Capetti²

2010

A&A

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“…Galaxy color is the easiest parameter to measure among those that exhibit a distinctive bi-modality: spectral class, morphology, star formation rates and metallicities (see Strateva et al 2001;Mignoli et al 2009). Therefore it is the simplest to adopt in parametrizing the differences between evolution of groups and field or isolated galaxies.…”

Section: Measuring F Bluementioning

confidence: 99%

The zCOSMOS redshift survey: how group environment alters global downsizing trends

Iovino¹,

Cucciati

Scodeggio

et al. 2009

A&A

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Context. Groups of galaxies are a common environment, bridging the gap between starforming field galaxies and quiescent cluster galaxies. Within groups secular processes could be at play, contributing to the observed strong decrease of star formation with cosmic time in the global galaxy population. Aims. We took advantage of the wealth of information provided by the first ∼10 000 galaxies of the zCOSMOS-bright survey and its group catalogue to study in detail the complex interplay between group environment and galaxy properties. Methods. The classical indicator F blue , i.e., the fraction of blue galaxies, proved to be a simple but powerful diagnostic tool. We studied its variation for different luminosity and mass selected galaxy samples, divided as to define groups/field/isolated galaxy subsamples. Results. Using rest-frame evolving B-band volume-limited samples, the groups galaxy population exhibits significant blueing as redshift increases, but maintains a systematic difference (a lower F blue ) with respect to the global galaxy population, and an even larger difference with respect to the isolated galaxy population. However moving to mass selected samples it becomes apparent that such differences are largely due to the biased view imposed by the B-band luminosity selection, being driven by the population of lower mass, bright blue galaxies for which we miss the redder, equally low mass, counterparts. By carefully focusing the analysis on narrow mass bins such that mass segregation becomes negligible we find that only for the lowest mass bin explored, i.e., log(M * /M ) ≤ 10.6, does a significant residual difference in color remain as a function of environment, while this difference becomes negligible toward higher masses. Conclusions. Our results indicate that red galaxies of mass log(M * /M ) ≥ 10.8 are already in place at z ∼ 1 and do not exhibit any strong environmental dependence, possibly originating from so-called nature or internal mechanisms. In contrast, for lower galaxy masses and redshifts lower than z ∼ 1, we observe the emergence in groups of a population of nurture red galaxies: slightly deviating from the trend of the downsizing scenario followed by the global galaxy population, and more so with cosmic time. These galaxies exhibit signatures of group-related secular physical mechanisms directly influencing galaxy evolution. Our analysis implies that these mechanisms begin to significantly influence galaxy evolution after z ∼ 1, a redshift corresponding to the emergence of structures in which these mechanisms take place.

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“…This extended sample is considered from now on for the statistical comparison against a control sample consisting of 36 radio-loud sources with redshift z < 0.3, and covering the same range of optical and radio luminosities as the X-shaped sample. A control subsample of elliptical radio-loud sources with values of C Ca II > 0.25 and that qualify as early-type galaxies according to color-color diagnostics (i.e., location above the u-r galaxy type separator in a color-color diagram; Strateva et al 2001) is also considered for the statistical comparison (selection of both samples is described in detail in M11). The morphological classification based on visual inspection of SDSS images of this subsample of elliptical control sources agrees with the one based on the Ca II break and color-color diagram.…”

Section: Resultsmentioning

confidence: 99%

“…The host galaxy type can be inferred using a color-color diagram, obtained from the SDSS u, g, and r-band photometry. We apply a color-color distinction (Strateva et al 2001) to identify the type of the host galaxy in the 10 new X-shaped sources considered for the statistical analysis. The combined plot presented in Fig.…”

Section: Host Typementioning

confidence: 99%

Starbursts and black hole masses in X-shaped radio galaxies: Signatures of a merger event?

Mezcua

Chavushyan

Lobanov

2012

A&A

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We present new spectroscopic identifications of 12 X-shaped radio galaxies and use the spectral data to derive starburst histories and masses of the nuclear supermassive black holes in these galaxies. The observations were done with the 2.1-m telescope of the Observatorio Astronómico Nacional at San Pedro Mártir, México. The new spectroscopic results extend the sample of X-shaped radio galaxies studied with optical spectroscopy. We show that the combined sample of the X-shaped radio galaxies has statistically higher black-hole masses and older episodes of star formation than a control sample of canonical double-lobed radio sources with similar redshifts and luminosities. The data reveal enhanced star-formation activity in the X-shaped sample on the timescales expected in galactic mergers. We discuss the results obtained in the framework of the merger scenario.

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Color Separation of Galaxy Types in the Sloan Digital Sky Survey Imaging Data

Cited by 1,493 publications

References 21 publications

Spectro-photometric properties of the bulk of the radio-loud AGN population

Spectro-photometric properties of the bulk of the radio-loud AGN population

The zCOSMOS redshift survey: how group environment alters global downsizing trends

Starbursts and black hole masses in X-shaped radio galaxies: Signatures of a merger event?

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