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...
Based on a combined analysis of SDSS imaging and CALIFA integral field spectroscopy data, we report on the detection of faint (24 < µ r mag/ < 26) star-forming spiral-arm-like features in the periphery of three nearby early-type galaxies (ETGs). These features are of considerable interest because they document the still ongoing inside-out growth of some local ETGs and may add valuable observational insight into the origin and evolution of spiral structure in triaxial stellar systems. A characteristic property of the nebular component in the studied ETGs, classified i+, is a two-radial-zone structure, with the inner zone that displays faint (EW(Hα) 1 Å) low-ionization nuclear emission-line region (LINER) properties, and the outer one (3 Å < EW(Hα) < ∼ 20 Å) H-region characteristics. This spatial segregation of nebular emission in two physically distinct concentric zones calls for an examination of aperture effects in studies of type i+ ETGs with single-fiber spectroscopic data.
Context. A key subject in extragalactic astronomy concerns the chronology and driving mechanisms of bulge formation in late-type galaxies (LTGs). The standard scenario distinguishes between classical bulges and pseudo-bulges (CBs and PBs, respectively), the first thought to form monolithically prior to disks and the second gradually out of disks. These two bulge formation routes obviously yield antipodal predictions on the bulge age and bulge-to-disk age contrast, both expected to be high (low) in CBs (PBs). Aims. Our main goal is to explore whether bulges in present-day LTGs segregate into two evolutionary distinct classes, as expected from the standard scenario. Other questions motivating this study center on evolutionary relations between LTG bulges and their hosting disks, and the occurrence of accretion-powered nuclear activity as a function of bulge stellar mass M and stellar surface density Σ . Methods. In this study we have combined three techniques -surface photometry, spectral modeling of integral field spectroscopy data and suppression of stellar populations younger than an adjustable age cutoff with the code REMOVEYOUNG (RY) -toward a systematic analysis of the physical and evolutionary properties (e.g., M , Σ and mass-weighted stellar age t M and metallicity Z M , respectively) of a representative sample of 135 nearby (≤130 Mpc) LTGs from the CALIFA survey that cover a range between 10 8.9 M and 10 11.5 M in total stellar mass M ,T . In particular, the analysis here revolves around <δµ 9G >, a new distance-and formally extinction-independent measure of the contribution by stellar populations of age ≥9 Gyr to the mean r-band surface brightness of the bulge. We argue that <δµ 9G > offers a handy semi-empirical tracer of the physical and evolutionary properties of LTG bulges and a promising means for their characterization. Results. The essential insight from this study is that LTG bulges form over three dex in M and more than one dex in Σ a tight continuous sequence of increasing <δµ 9G > with increasing M , Σ , t M and Z M . Along this continuum of physical and evolutionary properties, our sample spans a range of ∼4 mag in <δµ 9G >: high-<δµ 9G > bulges are the oldest, densest and most massive ones ( t M ∼11.7 Gyr, Σ > 10 9 M kpc −2 , M ≥ 10 10 M ), whereas the opposite is the case for low-<δµ 9G > bulges ( t M ∼7 Gyr) that generally reside in low-mass LTGs. Furthermore, we find that the bulge-to-disk age and metallicity contrast, as well as the bulge-todisk mass ratio, show a positive trend with M ,T , raising from, respectively, ∼0 Gyr, ∼0 dex and 0.25 to ∼3 Gyr, ∼0.3 dex and 0.67 across the mass range covered by our sample. Whereas gas excitation in lower-mass ( 10 9.7 M ) bulges is invariably dominated by star formation (SF), LINER-and Seyfert-specific emission-line ratios were exclusively documented in high-mass ( 10 10 M ), high-Σ ( 10 9 M kpc −2 ) bulges. This is in agreement with previous work and consistent with the notion that the Eddington ratio or the black hole-to-bulge mass rati...
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