Central Velocity Dispersion Research Articles

How ‘cold’ are the stellar discs of superthin galaxies?

ABSTRACT Superthin galaxies are a class of bulgeless, low surface brightness galaxies with strikingly high values of planar-to-vertical axes ratio $\rm (b/a\gt 10\!-\!20)$, possibly indicating the presence of an ultracold stellar disc. Using the multicomponent galactic disc model of gravitationally coupled stars and gas in the force field of the dark matter halo as well as the stellar dynamical code AGAMA (Action-based Galaxy Modelling Architecture), we determine the vertical velocity dispersion of stars and gas as a function of galactocentric radius for five superthin galaxies (UGC 7321, IC 5249, FGC 1540, IC2233, and UGC00711) using observed stellar and atomic hydrogen (H i) scale heights as constraints, using a Markov chain Monte Carlo Method. We find that the central vertical velocity dispersion for the stellar disc in the optical band varies between σ0s ∼ 10.2−18.4 $\rm {kms}\,^{-1}$ and falls off with an exponential scale length of 2.6–3.2 Rd where Rd is the exponential stellar disc scale length. Interestingly, in the 3.6 μm, the same, averaged over the two components of the stellar disc, varies between 5.9 and 11.8 $\rm {kms}\,^{-1}$, both of which confirm the presence of ‘ultracold’ stellar discs in superthin galaxies. Interestingly, the global median of the multicomponent disc dynamical stability parameter QN of our sample superthins is found to be 5 ± 1.5, which higher than the global median value of 2.2 ± 0.6 for a sample of spiral galaxies.

MOCCA Survey Database: extra Galactic globular clusters. I. Method and first results

ABSTRACT Over the last few decades, exhaustive surveys of extra Galactic globular clusters (EGGCs) have become feasible. Only recently, limited kinematical information of globular clusters (GCs) were available through Gaia Data Release 2 spectroscopy and also proper motions. On the other hand, simulations of GCs can provide detailed information about the dynamical evolution of the system. We present a preliminary study of EGGCs’ properties for different dynamical evolutionary stages. We apply this study to 12-Gyr-old GCs simulated as part of the MOCCA Survey Database. Mimicking observational limits, we consider only a subsample of the models in the data base, showing that it is possible to represent observed Milky Way GCs. In order to distinguish between different dynamical states of EGGCs, at least three structural parameters are necessary. The best distinction is achieved by considering the central parameters, those being observational core radius, central surface brightness, ratio between central and half-mass velocity dispersion, or similarly considering the central colour, the central V magnitude, and the ratio between central and half-mass radius velocity dispersion, although such properties could be prohibitive with current technologies. A similar but less solid result is obtained considering the average properties at the half-light radius, perhaps accessible presently in the Local Group. Additionally, we mention that the colour spread in EGGCs due to internal dynamical models, at fixed metallicity, could be just as important due to the spread in metallicity.

Revealing the relation between black hole growth and host-galaxy compactness among star-forming galaxies

ABSTRACT Recent studies show that a universal relation between black hole (BH) growth and stellar mass (M⋆) or star formation rate (SFR) is an oversimplification of BH–galaxy coevolution, and that morphological and structural properties of host galaxies must also be considered. Particularly, a possible connection between BH growth and host-galaxy compactness was identified among star-forming (SF) galaxies. Utilizing ≈6300 massive galaxies with I814W < 24 at z < 1.2 in the Cosmic Evolution Survey (COSMOS) field, we perform systematic partial correlation analyses to investigate how sample-averaged BH accretion rate ($\rm \overline{BHAR}$) depends on host-galaxy compactness among SF galaxies, when controlling for morphology and M⋆ (or SFR). The projected central surface mass density within 1 kpc, Σ1, is utilized to represent host-galaxy compactness in our study. We find that the $\rm \overline{BHAR}$–Σ1 relation is stronger than either the $\rm \overline{BHAR}$–M⋆ or $\rm \overline{BHAR}$–SFR relation among SF galaxies, and this $\rm \overline{BHAR}$–Σ1 relation applies to both bulge-dominated galaxies and galaxies that are not dominated by bulges. This $\rm \overline{BHAR}$–Σ1 relation among SF galaxies suggests a link between BH growth and the central gas density of host galaxies on the kpc scale, which may further imply a common origin of the gas in the vicinity of the BH and in the central ∼kpc of the galaxy. This $\rm \overline{BHAR}$–Σ1 relation can also be interpreted as the relation between BH growth and the central velocity dispersion of host galaxies at a given gas content (i.e. gas mass fraction), indicating the role of the host-galaxy potential well in regulating accretion on to the BH.

Young stellar population gradients in central cluster galaxies from NUV and optical spectroscopy

ABSTRACT Central cluster galaxies are the largest and most massive galaxies in the Universe. Although they host very old stellar populations, several studies found the existence of blue cores in some BCGs indicating ongoing star formation. We analyse VLT/X-Shooter stacked spectra of 6 nearby massive central galaxies with high central velocity dispersions (σ > 300 km s−1) at different galactocentric distances. We quantify the young stellar population out to 4 kpc by fitting near-UV and optical absorption line indices with predictions of composite stellar populations modelled by an old and a young stellar component. We also use IMF-sensitive indices since these galaxies have been found to host a bottom-heavy IMF in their central regions. We derive negative young stellar populations gradients, with mass fractions of stars younger than 1 Gyr decreasing with galactocentric distance, from 0.70 per cent within 0.8 kpc to zero beyond 2 kpc. We also measure the mass fraction in young stars for individual galaxies in the highest S/N central regions. All the galaxies have young components of less than one percent. Our results clearly suggest that the star formation in massive central cluster galaxies takes place in their galaxy cores (<2 kpc), which, with deeper gravitational potential wells, are capable of retaining more gas. Among the possible sources for the gas required to form these young stars, our results are consistent with an in situ origin via stellar evolution, which is sufficient to produce the observed young stellar populations.

Tracing Dark Matter Halos with Satellite Kinematics and the Central Stellar Velocity Dispersion of Galaxies

Abstract It has been suggested that the central stellar velocity dispersion of galaxies can trace dark matter halo mass directly. We test this hypothesis using a complete spectroscopic sample of isolated galaxies surrounded by faint satellite galaxies from the Sloan Digital Sky Survey Data Release 12. We apply a friends-of-friends algorithm with projected linking length and radial velocity linking length km s−1 to construct our sample. Our sample includes 2807 isolated galaxies with 3417 satellite galaxies at . We divide the sample into two groups based on the primary galaxy color: red and blue primary galaxies separated at . The central stellar velocity dispersions of the primary galaxies are proportional to the luminosities and stellar masses of the same galaxies. Stacking the sample based on the central velocity dispersion of the primary galaxies, we derive the velocity dispersions of their satellite galaxies, which trace the dark matter halo mass of the primary galaxies. The system velocity dispersion of the satellite galaxies shows a remarkably tight correlation with the central velocity dispersion of the primary galaxies for both red and blue samples. In particular, the slope of the relation is identical to 1 for red primary systems. This tight relation suggests that the central stellar velocity dispersion of galaxies is indeed an efficient and robust tracer for dark matter halo mass. We provide empirical relations between the central stellar velocity dispersion and the dark matter halo mass.

Study of central intensity ratio of early-type galaxies from low-density environment

ABSTRACT We present correlations involving central intensity ratio (CIR) of 52 early-type galaxies, including 24 ellipticals and 28 lenticulars, selected from low-density environment in the nearby (<30 Mpc) universe. CIR is found to be negatively and significantly correlated with the mass of the central supermassive black hole, central velocity dispersion, absolute B-band magnitude, stellar bulge mass, and central Mg2 index of the host galaxy. The study proposes the use of CIR as a simple, fast, and efficient photometric tool for exploring the co-evolution scenario existing in galaxies.

The Velocity Dispersion Function for Quiescent Galaxies in Nine Strong-lensing Clusters

Abstract We measure the central stellar velocity dispersion function for quiescent galaxies in a set of nine northern clusters in the redshift range 0.18 < z < 0.29 and with strong lensing arcs in Hubble Space Telescope images. The velocity dispersion function links galaxies directly to their dark matter halos. From dense SDSS and MMT/Hectospec spectroscopy, we identify 222–463 spectroscopic members in each cluster. We derive physical properties of cluster members including redshift, , and central stellar velocity dispersion and we include a table of these measurements for 3419 cluster members. We construct the velocity dispersion functions for quiescent galaxies with > 1.5 and within R 200. The cluster velocity dispersion functions all show excesses at σ ≳ 250 km s−1 compared to the field velocity dispersion function. The velocity dispersion function slope at large velocity dispersion (σ > 160 km s−1) is steeper for more massive clusters, consistent with the trend observed for cluster luminosity functions. The spatial distribution of galaxies with large velocity dispersion at radii larger than R 200 further underscores the probable major role of dry mergers in the growth of massive cluster galaxies during cluster assembly.

The Relative Role of Bars and Galaxy Environments in AGN Triggering of SDSS Spirals

Abstract We quantify the relative role of galaxy environment and bar presence on AGN triggering in face-on spiral galaxies using a volume-limited sample with 0.02 < z < 0.055, M r < 19.5, and σ > 70 selected from Sloan Digital Sky Survey (SDSS) Data Release 7. To separate their possible entangled effects, we divide the sample into bar and non-bar samples, and each sample is further divided into three environment cases of isolated galaxies, interacting galaxies with a pair, and cluster galaxies. The isolated case is used as a control sample. For these six cases, we measure AGN fractions at a fixed central star formation rate and central velocity dispersion, σ. We demonstrate that the internal process of the bar-induced gas inflow is more efficient in AGN triggering than the external mechanism of the galaxy interactions in groups and cluster outskirts. The significant effects of bar instability and galaxy environments are found in galaxies with a relatively less massive bulge. We conclude that from the perspective of AGN–galaxy coevolution, a massive black hole is one of the key drivers of spiral galaxy evolution. If it is not met, a bar instability helps the evolution, and in the absence of bars, galaxy interactions/mergers become important. In other words, in the presence of a massive central engine, the role of the two gas inflow mechanisms is reduced or almost disappears. We also find that bars in massive galaxies are very decisive in increasing AGN fractions when the host galaxies are inside clusters.

How do central and satellite galaxies quench? – Insights from spatially resolved spectroscopy in the MaNGA survey

ABSTRACT We investigate how star formation quenching proceeds within central and satellite galaxies using spatially resolved spectroscopy from the SDSS-IV MaNGA DR15. We adopt a complete sample of star formation rate surface densities (ΣSFR), derived in Bluck et al. (2020), to compute the distance at which each spaxel resides from the resolved star forming main sequence (ΣSFR − Σ* relation): ΔΣSFR. We study galaxy radial profiles in ΔΣSFR, and luminosity weighted stellar age (AgeL), split by a variety of intrinsic and environmental parameters. Via several statistical analyses, we establish that the quenching of central galaxies is governed by intrinsic parameters, with central velocity dispersion (σc) being the most important single parameter. High mass satellites quench in a very similar manner to centrals. Conversely, low mass satellite quenching is governed primarily by environmental parameters, with local galaxy overdensity (δ5) being the most important single parameter. Utilizing the empirical MBH − σc relation, we estimate that quenching via AGN feedback must occur at $M_{\rm BH} \ge 10^{6.5-7.5} \, \mathrm{M}_{\odot }$, and is marked by steeply rising ΔΣSFR radial profiles in the green valley, indicating ‘inside-out’ quenching. On the other hand, environmental quenching occurs at overdensities of 10–30 times the average galaxy density at z∼ 0.1, and is marked by steeply declining ΔΣSFR profiles, indicating ‘outside-in’ quenching. Finally, through an analysis of stellar metallicities, we conclude that both intrinsic and environmental quenching must incorporate significant starvation of gas supply.

Central velocity dispersion catalogue of LAMOST-DR7 galaxies

ABSTRACT The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is a major facility to carry out spectroscopic surveys for cosmology and galaxy evolution studies. The seventh data release of the LAMOST ExtraGAlactic Survey (LEGAS) is currently available and including redshifts of 193 361 galaxies. These sources are spread over $\sim 11\, 500$ deg2 of the sky, largely overlapping with other imaging (SDSS and HSC) and spectroscopic (BOSS) surveys. The estimated depth of the galaxy sample, r ∼ 17.8, the high signal-to-noise ratio, and the spectral resolution R = 1800, make the LAMOST spectra suitable for galaxy velocity dispersion (VD) measurements, which are invaluable to study the structure and formation of galaxies and to determine their central dark matter content. We present the first estimates of central VD of $\sim 86\, 000$ galaxies in LAMOST footprint. We have used a wrap-up procedure to perform the spectral fitting using ppxf, and derive VD measurements. Statistical errors are also assessed by comparing LAMOST VD estimates with the ones of SDSS and BOSS over a common sample of $\sim 51\, 000$ galaxies. The two data sets show a good agreement, within the statistical errors, in particular when VD values are corrected to 1 effective radius aperture. We also present a preliminary mass–σ relation and find consistency with previous analyses based on local galaxy samples. These first results suggest that LAMOST spectra are suitable for galaxy VD measurements to complement the available catalogues of galaxy internal kinematics in the Northern hemisphere. We plan to expand this analysis to next LAMOST data releases.

Infrared Emission from Cold Gas Dusty Disks in Massive Ellipticals

Abstract What is the expected infrared output of elliptical galaxies? We report the latest findings obtained in this high time resolution (∼10 yr) and high spatial resolution (2.5 pc at center) study. We add a set of grain physics to the Massive active galactic nucleus (AGN) Controlled Ellipticals Resolved code, including (a) dust grains made in passive stellar evolution; (b) dust grain growth due to collision and sticking; (c) grain destruction due to thermal sputtering; (d) dust cooling of hot gas via inelastic collisions; and (e) radiation pressure on dust grains. The code improvements enable us to analyze metal depletion and AGN obscuration due to dust, and to assess its infrared output. We simulate a representative massive elliptical galaxy of a central stellar velocity dispersion ∼260 km s−1 and modest rotation. We find that: (1) the circumnuclear disk (∼1 kpc in diameter) is dusty in its outer region where most of the metals are contained in dust grains, while in the inner disk, dust grains are mostly destroyed by the AGN irradiation; (2) the dusty disk is optically thick to both the starlight within the disk and the radiation from the central AGN; thus the AGN is obscured behind the disk, and the covering factor is ∼0.2; and (3) the duty cycles of the AGN activities, star formation, and the dust infrared luminosity roughly match observations; e.g., in most of its lifetime, the simulated galaxy is a stereotypical “quiescent” elliptical galaxy with , but it can reach ≳1046 erg s−1 during outbursts with a star formation rate .

A robust two-parameter description of the stellar profile of elliptical galaxies

Context. The stellar density profile of a galaxy is typically summarised with two numbers: the total stellar mass and half-light radius. The total mass of a galaxy, however, is not a well-defined quantity, due to the finite depth of photometric observations and the arbitrariness of the distinction between galaxy and diffuse intra-group light. This limits our ability to make accurate comparisons between models and observations. Aims. I wish to provide a more robust two-parameter description of the stellar density distribution of elliptical galaxies, in terms of quantities that can be measured unambiguously. Methods. I propose using the stellar mass enclosed within 10 kpc in projection, M*,10, and the mass-weighted stellar density slope within the same aperture, Γ*,10, for this purpose. I measured the distribution in M*,10 and Γ*,10 of a sample of elliptical galaxies from the Sloan Digital Sky Survey and the Galaxy And Mass Assembly survey, using photometry from the Hyper Suprime-Cam survey. I measured, at fixed (M*,10, Γ*,10), what the spread is in the galaxy surface brightness profile and central stellar velocity dispersion within the sample. As a first application, I then compared the observed M*,10 − Γ*,10 relation of elliptical galaxies with that of similarly selected galaxies in the EAGLE REFERENCE simulation. Results. The pair of values of (M*,10, Γ*,10) can be used to predict the stellar density profile in the inner 10 kpc of a galaxy with better than 20% accuracy. Similarly, M*,10 and Γ*,10 can be combined to obtain a proxy for stellar velocity dispersion that is at least as good as the stellar mass fundamental plane. The average stellar density slope of EAGLE elliptical galaxies matches that of observed ones at M*,10 = 1011 M⊙ well, but the EAGLE M*,10 − Γ*,10 relation is shallower and has a larger intrinsic scatter compared to observations. Conclusions. This new parameterisation of the stellar density profile of massive elliptical galaxies provides a more robust way of comparing results from different photometric surveys and from hydrodynamical simulations, with respect to a description based on total stellar mass and half-light radius.

Velocity Dispersions of Massive Quiescent Galaxies from Weak Lensing and Spectroscopy*

Abstract We use MMT spectroscopy and deep Subaru Hyper Suprime-Cam (HSC) imaging to compare the spectroscopic central stellar velocity dispersion of quiescent galaxies with the effective dispersion of the dark matter halo derived from the stacked lensing signal. The spectroscopic survey (the Smithsonian Hectospec Lensing Survey) provides a sample of 4585 quiescent galaxy lenses with measured line-of-sight central stellar velocity dispersion (σ SHELS) that is more than 85% complete for R < 20.6, D n 4000 > 1.5 and M ⋆ > 109.5 M ⊙. The median redshift of the sample of lenses is 0.32. We measure the stacked lensing signal from the HSC deep imaging. The central stellar velocity dispersion is directly proportional to the velocity dispersion derived from the lensing σ Lens, . The independent spectroscopic and weak lensing velocity dispersions probe different scales, ∼3 kpc and ≳100 kpc, respectively, and strongly indicate that the observable central stellar velocity dispersion for quiescent galaxies is a good proxy for the velocity dispersion of the dark matter halo. We thus demonstrate the power of combining high-quality imaging and spectroscopy to shed light on the connection between galaxies and their dark matter halos.

The cosmic evolution of the stellar mass–velocity dispersion relation of early-type galaxies

ABSTRACT We study the evolution of the observed correlation between central stellar velocity dispersion σe and stellar mass M* of massive ($M_*\gtrsim 3\times 10^{10}\, \mathrm{M_\odot}$) early-type galaxies (ETGs) out to redshift z ≈ 2.5, taking advantage of a Bayesian hierarchical inference formalism. Collecting ETGs from state-of-the-art literature samples, we build a fiducial sample (0 ≲ z ≲ 1), which is obtained with homogeneous selection criteria, but also a less homogeneous extended sample (0 ≲ z ≲ 2.5). Based on the fiducial sample, we find that at z ≲ 1 the M*–σe relation is well represented by $\sigma _{\mathrm{e}}\propto M_*^{\beta }(1+z)^{\zeta}$, with β ≃ 0.18 independent of redshift and ζ ≃ 0.4 (at a given M*, σe decreases for decreasing z, for instance by a factor of ≈1.3 from z = 1 to z = 0). When the slope β is allowed to evolve, we find it increasing with redshift: β(z) ≃ 0.16 + 0.26log (1 + z) describes the data as well as constant β ≃ 0.18. The intrinsic scatter of the M*–σe relation is ≃0.08 dex in σe at given M*, independent of redshift. Our results suggest that, on average, the velocity dispersion of individual massive (M* ≳ 3 × 1011M⊙) ETGs decreases with time while they evolve from z ≈ 1 to z ≈ 0. The analysis of the extended sample, over the wider redshift range 0 ≲ z ≲ 2.5, leads to results similar to that of the fiducial sample, with slightly stronger redshift dependence of the normalization (ζ ≃ 0.5) and weaker redshift dependence of the slope (dβ/dlog (1 + z) ≃ 0.18) when β varies with time. At z = 2 ETGs with $M_*\approx 10^{11}\, \mathrm{M_\odot}$ have, on average, ≈1.7 higher σe than ETGs of similar stellar mass at z = 0.

A Black Hole Feedback Valve in Massive Galaxies

Abstract Star formation in the universe’s most massive galaxies proceeds furiously early in time but then nearly ceases. Plenty of hot gas remains available but does not cool and condense into star-forming clouds. Active galactic nuclei (AGNs) release enough energy to inhibit cooling of the hot gas, but energetic arguments alone do not explain why quenching of star formation is most effective in high-mass galaxies. In fact, optical observations show that quenching is more closely related to a galaxy’s central stellar velocity dispersion (σ v ) than to any other characteristic. Here we show that high σ v is critical to quenching because a deep central potential well maximizes the efficacy of AGN feedback. In order to remain quenched, a galaxy must continually sweep out the gas ejected from its aging stars. Supernova heating can accomplish this task as long as the AGN sufficiently reduces the gas pressure of the surrounding circumgalactic medium (CGM). We find that CGM pressure acts as the control knob on a valve that regulates AGN feedback and suggest that feedback power self-adjusts so that it suffices to lift the CGM out of the galaxy’s potential well. Supernova heating then drives a galactic outflow that remains homogeneous if . The AGN feedback can effectively quench galaxies with a comparable velocity dispersion, but feedback in galaxies with a much lower velocity dispersion tends to result in convective circulation and accumulation of multiphase gas within the galaxy.

Lessons on Star-forming Ultra-diffuse Galaxies from the Stacked Spectra of the Sloan Digital Sky Survey

Abstract We investigate the on-average properties for 28 star-forming ultra-diffuse galaxies (UDGs) located in low-density environments, by stacking their spectra from the Sloan Digital Sky Survey. These relatively isolated UDGs, with stellar masses of , have the on-average total stellar metallicity [M/H] ∼ −0.82 ± 0.14, iron metallicity [Fe/H] ∼ −1.00 ± 0.16, stellar age t * ∼ 5.2 ± 0.5 Gyr, α-enhancement [α/Fe] ∼ 0.24 ± 0.10, and oxygen abundance 12+log(O/H) ∼ 8.16 ± 0.06, as well as central stellar velocity dispersion 54 ± 12 km s−1. On the star formation rate versus stellar mass diagram, these UDGs are located lower than the extrapolated star-forming main sequence from the massive spirals, but roughly follow the main sequence of low-surface-brightness dwarf galaxies. We find that these star-forming UDGs are not particularly metal-poor or metal-rich for their stellar masses, as compared with the metallicity–mass relations of the nearby typical dwarfs. With the UDG data of this work and previous studies, we also find a coarse correlation between [Fe/H] and magnesium-element enhancement [Mg/Fe] for UDGs: [Mg/Fe] ≃ −0.43(±0.26) [Fe/H] −0.14(±0.40).

Properties of the Hot Ambient Medium of Early-type Galaxies Hosting Powerful Radio Sources

Abstract We present an archival analysis of Chandra X-ray observations for 12 nearby early-type galaxies hosting radio sources with radio power >1023 W Hz−1 at 1.4 GHz, similar to the radio power of the radio source in NGC 4261. Previously, in a similar analysis of eight nearby X-ray and optically bright elliptical galaxies, Werner et al. found that NGC 4261 exhibited unusually low central gas entropy compared to the full sample. In the central 0.3 kpc of NGC 4261, the ratio of cooling time to freefall time (t cool/t ff) is less than 10, indicating that cold clouds may be precipitating out of the hot ambient medium and providing fuel for accretion in the central region. NGC 4261 also hosts the most powerful radio source in the original sample. Because NGC 4261 may represent an important phase during which powerful feedback from a central active galactic nucleus (AGN) is fueled by multiphase condensation in the central kiloparsec, we searched the Chandra archive for analogs to NGC 4261. We present entropy profiles of those galaxies, as well as profiles of t cool/t ff. We find that one of them, IC 4296, exhibits properties similar to NGC 4261, including the presence of only single-phase gas outside of r ∼ 2 kpc and a similar central velocity dispersion. We compare the properties of NGC 4261 and IC 4296 to hydrodynamic simulations of AGN feedback fueled by precipitation. Over the course of those simulations, the single-phase galaxy has an entropy gradient that remains similar to the entropy profiles inferred from our observations.

Circumnuclear regions of different BPT types in star-forming MaNGA galaxies: AGN detectability

We consider the circumnuclear regions of star-forming MaNGA galaxies. The spaxels spectra are classified as active-galactic-nucleus-like (AGN-like), H II-region-like (or SF-like), and intermediate (INT) spectra according to their positions on the Baldwin-Phillips-Terlevich (BPT) diagram. There are the following four configurations of the radiation distributions in the circumnuclear regions in (massive) galaxies: (1) AGN+INT, the innermost region of the AGN-like radiation is surrounded by a ring of radiation of the intermediate type; (2) INT, the central area of radiation of the intermediate type; (3) SF+INT, the inner region of the H II-region-like radiation is surrounded by a ring of radiation of the intermediate type; and (4) SF, the central area of the H II-region-like radiation only. The low ionization nuclear emission line regions (LINERs) of configurations 1 and 2 are examined. The spaxel spectra of the LINERs form a sequences on the BPT diagram, that is, they lie along the known AGN-SF mixing line trajectories. The diagnostic line ratios of the spaxels spectra change smoothly with radius, from AGN-like (or INT) line ratios at the galactic center to H II-region-like at larger galactocentric distances. This is in agreement with the paradigm that the LINERs are excited by AGN activity. We found that the AGN and INT radiation in the circumnuclear region is accompanied by an enhanced gas velocity dispersionσgas. The radius of the area of the AGN and INT radiation is similar to the radius of the area with enhancedσgas, and the centralσgas, ccorrelates with the luminosity of the AGN+INT area. We assume that the gas velocity dispersion can serve as an indicator of the AGN activity. An appreciable enhancement ofσgas, cwas also measured in the SF-type centers of massive galaxies. The values ofσgas, cfor the SF-type centers partly overlap with those of the AGN-type centers. This suggests that the manifestation of the circumnuclear region as AGN or as SF on the BPT diagram depends not only on the value ofσgas, c(the level of the AGN activity) but it is also governed by an additional parameter(s). We find that there is a demarcation line between the positions of the AGN-type and SF-type objects on the central gas velocity dispersion – central Hαsurface brightness diagram, in the sense that an object with a given value ofσgas, cis an AGN-type only if the central Hαsurface brightness is lower than some value.

Dependence of the Fundamental Plane of Early-type Galaxies on Age and Internal Structure

Abstract We investigate the scatter in the fundamental plane (FP) of early-type galaxies (ETGs) and its dependence on age and internal structure of ETGs, using 16,283 ETGs with M r ≤ −19.5 and 0.025 ≤ z < 0.055 in Sloan Digital Sky Survey data. We use the relation between the age of ETGs and photometric parameters such as color, absolute magnitude, and central velocity dispersion of ETGs and find that the scatter in the FP depends on age. The FP of old ETGs with age ≳9 Gyr has a smaller scatter of ∼0.06 dex (∼14%), while that of young ETGs with age ≲6 Gyr has a larger scatter of ∼0.075 dex (∼17%). In the case of young ETGs, less compact ETGs have a smaller scatter in the FP (∼0.065 dex; ∼15%) than more compact ones (∼0.10 dex; ∼23%). On the other hand, the scatter in the FP of old ETGs does not depend on the compactness of galaxy structure. Thus, among the subpopulations of ETGs, compact young ETGs have the largest scatter in the FP. This large scatter in compact young ETGs is caused by ETGs that have low dynamical mass-to-light ratio (M dyn/L) and blue color in the central regions. By comparing with a simple model of the galaxy that has experienced a gas-rich major merger, we find that the scenario of recent gas-rich major merger can reasonably explain the properties of the compact young ETGs with excessive light for a given mass (low M dyn/L) and blue central color.

Measuring the mass of the supermassive black hole of the lenticular galaxy NGC 4546

ABSTRACT Most galaxies with a well-structured bulge host a supermassive black hole (SMBH) in their centre. Stellar kinematics models applied to adaptive optics (AO) assisted integral field unit observations are well-suited to measure the SMBH mass (MBH) and also the total mass-to-light ratio [(M/L)TOT] and possible anisotropies in the stellar velocity distribution in the central region of galaxies. In this work, we used new AO assisted Near-Infrared Integral Field Spectrometer (NIFS) observations and also photometric data from the Hubble Space Telescope Legacy Archive of the galaxy NGC 4546 in order to determine its SMBH mass. To do this, we applied the Jeans Anisotropic Modelling (JAM) method to fit the average second velocity moment in the line of sight $(\overline{v^2_{\mathrm{ los}}})$ of the stellar structure. In addition, we also obtained (M/L)TOT and the classical anisotropy parameter βz = 1-(σz/σR)2 for this object within a field of view of 200 × 200 pc2. Maps of the stellar radial velocity and of the velocity dispersion were built for this galaxy using the penalized pixel fitting (ppxf) technique. We applied the Multi Gaussian Expansion procedure to fit the stellar brightness distribution. Using JAM, the best-fitting model for $\overline{v^2_{\mathrm{ los}}}$ of the stellar structure was obtained with (M/L)TOT = 4.34 ± 0.07 (Johnson’s R band), MBH = (2.56 ± 0.16) × 108 M⊙ and βz = −0.015 ± 0.03 (3σ confidence level). With these results, we found that NGC 4546 follows the MBH × σ relation. We also measured the central velocity dispersion within a radius of 1 arcsec of this object as σc = 241 ± 2 km s−1.