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Register a new userExtended nebular emission in CALIFA early-type galaxies
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Jean Michel Gomes JMG
Publication date
2015
fields
Physics
and research's language is
English
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The morphological, spectroscopic and kinematical properties of the warm interstellar medium (wim) in early-type galaxies (ETGs) hold key observational constraints to nuclear activity and the buildup history of these massive quiescent systems. High-quality integral field spectroscopy (IFS) data with a wide spectral and spatial coverage, such as those from the CALIFA survey, offer a precious opportunity for advancing our understanding in this respect. We use deep IFS data from CALIFA (califa.caha.es) to study the wim over the entire extent and optical spectral range of 32 nearby ETGs. We find that all ETGs in our sample show faint (Halpha equivalent width EW~0.5...2 {AA}) extranuclear nebular emission extending out to >= 2 Petrosian_50 radii. Confirming and strengthening our conclusions in Papaderos et al. (2013) we argue that ETGs span a broad continuous sequence with regard to the properties of their wim, and they can be roughly subdivided into two characteristic classes. The first one (type i) comprises ETGs with a nearly constant EW~1-3 {AA} in their extranuclear component, in quantitative agreement with (even though, no proof for) the hypothesis of photoionization by pAGB stars. The second class (type ii) consists of virtually wim-evacuated ETGs with a large Lyman continuum (Lyc) photon escape fraction and a very low (<= 0.5 {AA}) EW in their nuclear zone. These two classes appear indistinguishable from one another by their LINER-specific emission-line ratios. Additionally, here we extend the classification by the class i+ which stands for a subset of type i ETGs with low-level star-fomation in contiguous spiral-arm like features in their outermost periphery. These faint features, together with traces of localized star formation in several type i&i+ systems point to a non-negligible contribution from young massive stars to the global ionizing photon budget in ETGs.
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We use deep integral field spectroscopy data from the CALIFA survey to study the warm interstellar medium (WIM) of 32 nearby early-type galaxies (ETGs). We propose a tentative subdivision of our sample ETGs into two groups, according to their Ha equivalent width (EW) and Lyman continuum (LyC) photon escape fraction (PLF). Type i ETGs show nearly constant EWs and a PLF~0, suggesting that photoionization by post-AGB stars is the main driver of their faint extranuclear nebular emission. Type ii ETGs are characterized by very low, outwardly increasing EWs, and a PLF as large as ~0.9 in their centers. Such properties point to a low, and inwardly decreasing WIM density and/or volume filling factor. We argue that, because of extensive LyC photon leakage, emission-line luminosities and EWs are reduced in type ii ETG nuclei by at least one order of magnitude. Consequently, the line weakness of these ETGs is by itself no compelling evidence for their containing merely weak (sub-Eddington accreting) active galactic nuclei (AGN). In fact, LyC photon escape, which has heretofore not been considered, may constitute a key element in understanding why many ETGs with prominent signatures of AGN activity in radio continuum and/or X-ray wavelengths show only faint emission lines and weak signatures of AGN activity in their optical spectra. The LyC photon escape, in conjunction with dilution of nuclear EWs by line-of-sight integration through a triaxial stellar host, can systematically impede detection of AGN in gas-poor galaxy spheroids through optical emission-line spectroscopy. We further find that type i and ii ETGs differ little (~0.4 dex) in their mean BPT line ratios, which in both cases are characteristic of LINERs. This potentially hints at a degeneracy of the projected, luminosity-weighted BPT ratios for the specific 3D properties of the WIM in ETGs. (abridged)
The morphological, spectroscopic and kinematical properties of the warm interstellar medium (wim) in early-type galaxies (ETGs) hold key observational constraints to nuclear activity and the buildup history of these massive, quiescent systems. High-quality integral field spectroscopy (IFS) data with a wide spectral and spatial coverage, such as those from the CALIFA survey, offer an unprecedented opportunity for advancing our understanding of the wim in ETGs. This article centers on a 2D investigation of the wim component in 32 nearby (<~150Mpc) ETGs from CALIFA, complementing a previous 1D analysis of the same sample (Papaderos et al. 2013; P13). We include here Halpha intensity and equivalent width (EW) maps and radial profiles, diagnostic emission-line ratios, besides ionized-gas and stellar kinematics. This study is supplemented by tau-ratio maps as an efficient means to quantify the role of photoionization by pAGB stars, as compared to other mechanisms (e.g., AGN, low-level star formation). Additionally, we extend the tentative classification proposed in P13 by the type i+, which is assigned to a subset of type i ETGs exhibiting ongoing low-level star-formation (SF) in their periphery. This finding along with faint traces of localized SF in the extranuclear component of several of our sample ETGs points to a non-negligible contribution by OB stars to the total ionizing budget. We also demonstrate that, at the typical emission-line detection threshold of ~2AA in previous studies, most of the extranuclear wim emission in an ETG may evade detection, which could in turn prompt its classification as an entirely gas-devoid system. This study adds further observational evidence for a considerable heterogeneity among ETGs with regard to the physical properties and 2D kinematics of the wim component, and underscores the importance of IFS studies over their entire optical extent.
The star formation main sequence (SFMS) is a tight relation between the galaxy star formation rate (SFR) and its total stellar mass ($M_star$). Early-type galaxies (ETGs) are often considered as low-SFR outliers of this relation. We study, for the first time, the separated distribution in the SFR vs. $M_star$ of bulges and discs of 49 ETGs from the CALIFA survey. This is achieved using C2D, a new code to perform spectro-photometric decompositions of integral field spectroscopy datacubes. Our results reflect that: i) star formation always occurs in the disc component and not in bulges; ii) star-forming discs in our ETGs are compatible with the SFMS defined by star forming galaxies at $z sim 0$; iii) the star formation is not confined to the outskirts of discs, but it is present at all radii (even where the bulge dominates the light); iv) for a given mass, bulges exhibit lower sSFR than discs at all radii; and v) we do not find a deficit of molecular gas in bulges with respect to discs for a given mass in our ETGs. We speculate our results favour a morphological quenching scenario for ETGs.
We perform spatially resolved stellar population analysis for a sample of 69 early-type galaxies (ETGs) from the CALIFA integral field spectroscopic survey, including 48 ellipticals and 21 S0s. We generate and quantitatively characterize profiles of light-weighted mean stellar age and metallicity within $lesssim 2R_e$, as a function of radius and stellar-mass surface density $mu_*$. We study in detail the dependence of profiles on galaxies global properties, including velocity dispersion $sigma_e$, stellar mass, morphology. ETGs are universally characterized by strong, negative metallicity gradients ($sim -0.3,text{dex}$ per $R_e$) within $1,R_e$, which flatten out moving towards larger radii. A quasi-universal local $mu_*$-metallicity relation emerges, which displays a residual systematic dependence on $sigma_e$, whereby higher $sigma_e$ implies higher metallicity at fixed $mu_*$. Age profiles are typically U-shaped, with minimum around $0.4,R_e$, asymptotic increase to maximum ages beyond $sim 1.5,R_e$, and an increase towards the centre. The depth of the minimum and the central increase anti-correlate with $sigma_e$. A possible qualitative interpretation of these observations is a two-phase scenario. In the first phase, dissipative collapse occurs in the inner $1,R_e$, establishing a negative metallicity gradient. The competition between the outside-in quenching due to feedback-driven winds and some form of inside-out quenching, possibly caused by central AGN feedback or dynamical heating, determines the U-shaped age profiles. In the second phase, the accretion of ex-situ stars from quenched and low-metallicity satellites shapes the flatter stellar population profiles in the outer regions.
The star formation rates (SFRs) in weak emission line (WEL) galaxies in a volume-limited ($0.02 < z < 0.05$) sample of blue early-type galaxies (ETGs) identified from SDSS, are constrained here using 1.4 GHz radio continuum emission. The direct detection of 1.4 GHz radio continuum emission is made in 8 WEL galaxies and a median stacking is performed on 57 WEL galaxies using VLA FIRST images. The median stacked 1.4 GHz flux density and luminosity are estimated as 79 $pm$ 19 $mu$Jy and 0.20 $pm$ 0.05 $times$ 10$^{21}$ W Hz$^{-1}$ respectively. The radio far-infrared correlation in 4 WEL galaxies suggests that the radio continuum emission from WEL galaxies is most likely due to star formation activities. The median SFR for WEL galaxies is estimated as 0.23 $pm$ 0.06 M$_{odot}$yr$^{-1}$, which is much less compared to SFRs ($0.5 - 50$ M$_{odot}$yr$^{-1}$) in purely star forming blue ETGs. The SFRs in blue ETGs are found to be correlated with their stellar velocity dispersions ($sigma$) and decreasing gradually beyond $sigma$ of $sim 100$ km s$^{-1}$. This effect is most likely linked with the growth of black hole and suppression of star formation via AGN feedback. The color differences between SF and WEL sub-types of blue ETGs appear to be driven to large extent by the level of current star formation activities. In a likely scenario of an evolutionary sequence between sub-types, the observed color distribution in blue ETGs can be explained best in terms of fast evolution through AGN feedback.
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