Warm ionized gas in CALIFA early-type galaxies

Abstract

Context. 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. Aims. This article centers on a 2D investigation of the wim component in 32 nearby ( < ∼ 150 Mpc) ETGs from CALIFA, complementing a previous 1D analysis of the same sample. Methods. The analysis presented here includes Hα intensity and equivalent width (EW) maps and radial profiles, diagnostic emission-line ratios, and ionized-gas and stellar kinematics. It is supplemented by τ-ratio maps, which are a more efficient means to quantify the role of photoionization by the post-AGB stellar component than alternative mechanisms (e.g., AGN, low-level star formation). Results. Confirming and strengthening our previous conclusions, we find that ETGs span a broad continuous sequence in the properties of their wim, exemplified by two characteristic classes. The first (type i) comprises systems with a nearly constant EW(Hα) in their extranuclear component, which quantitatively agrees with (but is no proof of) the hypothesis that photoionization by the post-AGB stellar component is the main driver of extended wim emission. The second class (type ii) stands for virtually wim-evacuated ETGs with a very low (≤0.5 Å), outwardly increasing EW(Hα). These two classes appear indistinguishable from one another by their LINER-specific emission-line ratios in their extranuclear component. Here we extend the tentative classification we proposed previously by the type i+, which is assigned to a subset of type i ETGs exhibiting ongoing low-level star-forming activity in their periphery. This finding along with faint traces of localized star formation in the extranuclear component of several of our sample galaxies points to a non-negligible contribution by OB stars to the global ionizing photon budget in ETGs. Additionally, our data again highlight the diversity of ETGs in their gaseous and stellar kinematics. While in one half of our sample, gas and stars show similar (yet not necessarily identical) velocity patterns that are both dominated by rotation along the major galaxy axis, our analysis also documents several cases of kinematical decoupling between gas and stars, or rotation along the minor galaxy axis. We point out that the generally very low ( < ∼ 1 Å) EW(Hα) of ETGs requires a careful quantitative assessment of potential observational and analysis biases in studies of their wim. With standard emission-line fitting tools, Balmer emission lines become progressively difficult to detect below an EW(Hα) ∼ 3 Å, therefore our current understanding of the presence and 2D emission patterns and kinematics of the diffuse wim ETGs may be severely incomplete. We demons...

Impact of an AGN featureless continuum on estimation of stellar population properties

“…However, as pointed out in Papaderos et al (2013) and Gomes et al (2016) (see also CGP16), standard BPT classification diagnostics become inapplicable in the case of virtually gas-evacuated galaxies where the bulk of the Lyman continuum radiation from an AGN eventually escapes without locally producing detectable optical line emission. This, together with dilution of nuclear emission-line EWs by the stellar component along the line of sight, may readily prevent detection of accretion-powered nuclear activity in an early-type galaxy (Papaderos et al 2013;Gomes et al 2016), which is then classified as retired/passive and included in automated PSS studies. The same may obviously apply to old classical bulges, many of which show faint nebular emission despite hosting a super-massive black hole whose accretion-powered energy release may result in significant contamination of the optical spectrum by an AGN PL component.…”

“…The code Starlight is widely used (e.g. Mateus et al 2006;Stasińska et al 2008;Cid Fernandes et al 2010Kehrig et al 2012;Benítez et al 2013;Papaderos et al 2013;Cid Fernandes et al 2014;Stasińska et al 2015; 2 Starlightv04: http://astro.ufsc.br/starlight/ Gomes et al 2016) and can be regarded as a good representative of the state of the art. It is important to bear in mind the main objective of this work is to quantify potential biases on fundamental physical properties of active galaxies estimated with purelystellar PSS that might rise owing to the introduction of a simple AGN model, as in Ciesla et al (2015).…”

“…Our work builds upon and extends a pilot investigation of biases in optical PSS modelling of early-type active galaxies showing a high Lyman continuum (LyC) photon escape fraction presented in Cardoso, (hereafter CGP16). The observational motivation behind this study comes from the estimation of a high (>90%) LyC photon escape fraction in early-type active galaxies by Papaderos et al (2013) and Gomes et al (2016), which, according to our current knowledge, host a super-massive black hole in their nuclei with expected accretion-powered activity. More generally, it is conceivable that the model framework adopted in this study is applicable to any other galaxy spheroid or spheroidal component (e.g.…”

Spectroscopic aperture biases in inside-out evolving early-type galaxies from CALIFA

“…For simplicity, the galaxy is constructed such as to display a constant age gradient ∇t = −0.5 Gyr/kpc, which imposes a maximum radius as a function of lookback time of R max (t) = (t 0 − t)/|∇t|, where t 0 is the galaxy formation lookback time. For the adopted model, the galaxy grows radially at a constant speed v ∼ 2km s −1 , and when it attains R max = 20 kpc (at z ∼ 0.3), the linear growth ceases, yielding a typical present-day ETG radius (e.g., Gomes et al 2015a). The Friedmann-Robertson-Walker cosmology with H 0 = 70 km s −1 Mpc −1 , Ω m = 0.3 and Ω Λ = 0.7 was adopted, yielding 13.52 Gyr for the age for the Universe.…”

“…For example, Kaviraj et al (2008) found that 10−15% of the stellar mass (M ) in these systems has been built in a declining SF process since z 1, a conclusion that appears to be in line with the small fraction (∼5.7%) of blue ETGs in the local Universe with estimated SF rates (SFRs) of between 0.5 and 50 M /yr (Schawinski et al 2009). It is also noteworthy in this context that spatially resolved studies of individual ETGs indicate an outward-increasing luminosity contribution from young-to-intermediate-age stellar populations (e.g., Fang et al 2012;Gomes et al 2015a). …”