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Register a new userThe host galaxy/AGN connection. Brightness profiles of early-type galaxies hosting Seyfert nuclei
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Alessandro Capetti
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[ABRIDGED] We recently presented evidence of a connection between the brightness profiles of nearby early-type galaxies and the properties of the AGN they host. The radio loudness of the AGN appears to be univocally related to the hosts brightness profile: radio-loud nuclei are only hosted by ``core galaxies while radio-quiet AGN are only found in ``power-law galaxies. We extend our analysis here to a sample of 42 nearby (V < 7000 km/s) Seyfert galaxies hosted by early-type galaxies. We used the available HST images to study their brightness profiles. Having excluded complex and highly nucleated galaxies, in the remaining 16 objects the brightness profiles can be successfully modeled with a Nuker law with a steep nuclear cusp characteristic of ``power-law galaxies (with logarithmic slope 0.51 - 1.07). This result is what is expected for these radio-quiet AGN based on our previous findings, thus extending the validity of the connection between brightness profile and radio loudness to AGN of a far higher luminosity. We explored the robustness of this result against a different choice of the analytic form for the brightness profiles, using a Sersic law. In no object could we find evidence of a central light deficit with respect to a pure Sersic model, the defining feature of ``core galaxies in this modeling framework. We conclude that, regardless of the modeling strategy, the dichotomy of AGN radio loudness can be univocally related to the hosts brightness profile. Our general results can be re-phrased as ``radio-loud nuclei are hosted by core galaxies, while radio-quiet AGN are found in non-core galaxies.
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This is the first of a series of three papers exploring the connection between the multiwavelength properties of AGNs in nearby early-type galaxies and the characteristics of their hosts. We selected two samples, both with high resolution 5 GHz VLA observations available and providing measurements down to 1 mJy level, reaching radio-luminosities as low as 10^19 W/Hz. We focus on the 116 radio-detected galaxies as to boost the fraction of AGN with respect to a purely optically selected sample. Here we present the analysis of the optical brightness profiles based on archival HST images, available for 65 objects. We separate early-type galaxies on the basis of the slope of their nuclear brightness profiles, into core and power-law galaxies following the Nukers scheme, rather than on the traditional morphological classification (i.e. into E and S0 galaxies). Our sample of AGN candidates is indistinguishable, when their brightness profiles are concerned, from galaxies of similar optical luminosity but hosting weaker (or no) radio-sources. We confirm previous findings that relatively bright radio-sources (L_r > 10^(21.5) W/Hz) are uniquely associated to core galaxies. However, below this threshold in radio-luminosity core and power-law galaxies coexist and they do not show any apparent difference in their radio-properties. Not surprisingly, since our sample is deliberately biased to favour the inclusion of active galaxies, we found a higher fraction of optically nucleated galaxies. Addressing the multiwavelength properties of these nuclei will be the aim of the two forthcoming papers.
This is the second of a series of three papers exploring the connection between the multiwavelength properties of AGN in nearby early-type galaxies and the characteristics of their hosts. In Capetti et al. (2005) we presented a study of the surface brightness profiles for the 65 objects with available archival HST images out of the 116 radio-detected galaxies. We classified early-type galaxies into ``core and ``power-law galaxies, discriminating on the basis of the slope of their nuclear brightness profiles. Here we focus on the 29 core galaxies (hereafter CoreG). We used HST and Chandra data to isolate their nuclear emission. The CoreG invariably host radio-loud nuclei, with an average radio-loudness parameter of Log R = 3.6. The optical and X-ray nuclear luminosities correlate with the radio-core power, smoothly extending the analogous correlations already found for low luminosity radio-galaxies. This supports the interpretation of a common non-thermal origin of the nuclear emission also for CoreG. The luminosities of the nuclear sources, most likely dominated by jet emission, set firm upper limits, as low as L/L_Edd = 10^{-9} in both the optical and X-ray band, on any emission from the accretion process. The similarity of CoreG and LLRG indicates that they are drawn from the same population of early-type galaxies. LLRG represent only the tip of the iceberg associated with (relatively) high activity levels, with CoreG forming the bulk of the population. A minimum black hole mass of M_{BH} = 10^8 M_sun is apparently associated with the radio-loud nuclei in both CoreG and LLRG, but this effect must be tested on a sample of less luminous galaxies, likely to host smaller black holes. ABRIDGED.
We present a study of 66 barred, early-type (S0-Sb) disk galaxies, focused on the disk surface brightness profile outside the bar region and the nature of Freeman Type I and II profiles, their origins, and their possible relation to disk truncations. This paper discusses the data and their reduction, outlines our classification system, and presents $R$-band profiles and classifications for all galaxies in the sample. The profiles are derived from a variety of different sources, including the Sloan Digital Sky Survey (Data Release 5). For about half of the galaxies, we have profiles derived from more than one telescope; this allows us to check the stability and repeatability of our profile extraction and classification. The vast majority of the profiles are reliable down to levels of mu_R ~ 27 mag arcsec^-2; in exceptional cases, we can trace profiles down to mu_R > 28. We can typically follow disk profiles out to at least 1.5 times the traditional optical radius R_25; for some galaxies, we find light extending to ~ 3 R_25. We classify the profiles into three main groups: Type I (single-exponential), Type II (down-bending), and Type III (up-bending). The frequencies of these types are approximately 27%, 42%, and 24%, respectively, plus another 6% which are combinations of Types II and III. We further classify Type II profiles by where the break falls in relation to the bar length, and in terms of the postulated mechanisms for breaks at large radii (classical trunction of star formation versus the influence of the Outer Lindblad Resonance of the bar). We also classify the Type III profiles by the probable morphology of the outer light (disk or spheroid). Illustrations are given for all cases. (Abridged)
[ABRIDGED] This is the third in a series of three papers exploring the connection between the multiwavelength properties of AGN in nearby early-type galaxies and the characteristics of their hosts. We selected 116 AGN candidates requiring a radio flux of 1 mJy. We classified the objects with HST images into ``core and ``power-law galaxies, on the basis of the nuclear slope of their brightness profiles. We used HST and Chandra data to isolate their nuclear emission to study the multiwavelength behaviour of their nuclei. The properties of the nuclei hosted by the 29 core galaxies were presented in Paper II. Core galaxies invariably host a radio-loud nucleus, with a median radio-loudness of Log R = 3.6 and an X-ray based radio loudness parameter of Log R,X = -1.3. Here we discuss the properties of the nuclei of the 22 ``power-law galaxies. They show a substantial excess of optical and X-ray emission with respect to core galaxies at the same level of radio luminosity. Conversely, their radio-loudness parameters, Log R ~ 1.6 and Log R,X ~ -3.3, are similar to those measured in Seyfert galaxies. Thus the radio-loudness of AGN hosted by early-type galaxies appears to be univocally related to the hosts brightness profile: radio-loud AGN are only hosted by core galaxies, while radio-quiet AGN are found only in power-law galaxies. The brightness profile is determined by the galaxys evolution, through its merger history; our results suggest that the same process sets the AGN flavour.
We combine the results from several HST investigations of the central structure of early-type galaxies to generate a large sample of parameterized surface photometry. The studies included were those that used the Nuker law to characterize the inner light distributions of the galaxies. The sample comprises WFPC1 and WFPC2 V band observations published earlier by our group, R band WFPC2 photometry of Rest et al., NICMOS H band photometry by Ravindranath et al. and Quillen et al., and the BCG WFPC2 I band photometry of Laine et al. The distribution of the logarithmic slopes of the central profiles strongly affirms that the central structure of elliptical galaxies with Mv < -19 is bimodal, based on both parametric and non-parametric analysis. At the HST resolution limit, most galaxies are either power-law systems, which have steep cusps in surface brightness, or core systems, which have shallow cusps interior to a steeper envelope brightness distribution. A rapid transition between the two forms occurs over the luminosity range -22 < Mv < -20, with cores dominating at the highest luminosities, and power-laws at the lowest. There are a few intermediate systems that have both cusp slopes and total luminosities that fall within the core/power-law transition, but they are rare and do not fill in the overall bimodal distribution of cusp slopes. These results are inconsistent with the Ferrarese et al. Virgo Cluster Survey (VCS) analysis. However, using galaxies common to the VCS samples, we demonstrate that the VCS models of the cusps are either a poor match to the observations or consist of forms fitted to the galaxy envelopes and extrapolated inward to the HST resolution limit.
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