IC 630: Piercing the Veil of the Nuclear Gas

IC 630 is a nearby early-type galaxy with a mass of $6 \times 10^{10} M_{\odot}$ with an intense burst of recent (6 Myr) star formation. It shows strong nebular emission lines, with radio and X-ray emission, which classifies it as an AGN. With VLT-SINFONI and Gemini North-NIFS adaptive optics observations (plus supplementary ANU 2.3m WiFeS optical IFU observations), the excitation diagnostics of the nebular emission species show no sign of standard AGN engine excitation; the stellar velocity dispersion also indicate that a super-massive black hole (if one is present) is small ($M_{\bullet} = 2.25 \times 10^{5}~M_{\odot}$). The luminosity at all wavelengths is consistent with star formation at a rate of about $1-2 M_{\odot}$/yr. We measure gas outflows driven by star formation at a rate of $0.18 M_{\odot}$/yr in a face-on truncated cone geometry. We also observe a nuclear cluster or disk and other clusters. Photo-ionization from young, hot stars is the main excitation mechanism for [Fe II] and hydrogen, whereas shocks are responsible for the H$_2$ excitation. Our observations are broadly comparable with simulations where a Toomre-unstable, self-gravitating gas disk triggers a burst of star formation, peaking after about 30 Myr and possibly cycling with a period of about 200 Myr.Comment: 32 pages, 19 figures Accepted for publication in Ap

Keck Cosmic Web Imager (KCWI) Spectra of Globular Clusters and Ultra Compact Dwarfs in the Halo of M87

Using the Keck Cosmic Web Imager we obtain spectra of several globular clusters (GCs), ultra compact dwarfs (UCDs) and the inner halo starlight of M87, at a similar projected galactocentric radius of $\sim$5 kpc. This enables us, for the first time, to apply the same stellar population analysis to the GCs, UCDs and starlight consistently to derive ages, metallicities and alpha-element abundances in M87. We find evidence for a dual stellar population in the M87 halo light, i.e an $\sim$80\% component by mass which is old and metal-rich and a $\sim$20\% component which is old but metal-poor. Two red GCs share similar stellar populations to the halo light suggesting they may have formed contemporaneously with the dominant halo component. Three UCDs, and one blue GC, have similar stellar populations, with younger mean ages, lower metallicities and near solar alpha-element abundances. Combined with literature data, our findings are consistent with the scenario that UCDs are the remnant nucleus of a stripped galaxy. We further investigate the discrepancy in the literature for M87's kinematics at large radii, favouring a declining velocity dispersion profile. This work has highlighted the need for more self-consistent studies of galaxy halos.Comment: 12 pages, 10 figures, accepted for publication in MNRA

Keck Cosmic Web Imager (KCWI) spectra of globular clusters and ultracompact dwarfs in the halo of M87

Using the Keck Cosmic Web Imager, we obtain spectra of several globular clusters (GCs), ultracompact dwarfs (UCDs), and the inner halo starlight of M87, at a similar projected galactocentric radius of ∼5 kpc. This enables us, for the first time, to apply the same stellar population analysis to the GCs, UCDs, and starlight consistently to derive ages, metallicities, and alpha-element abundances in M87. We find evidence for a dual stellar population in the M87 halo light, i.e. an ∼80 per cent component by mass that is old and metal-rich and a ∼20 per cent component that is old but metal-poor. Two red GCs share similar stellar populations to the halo light suggesting they may have formed contemporaneously with the dominant halo component. Three UCDs, and one blue GC, have similar stellar populations, with younger mean ages, lower metallicities, and near solar alpha-element abundances. Combined with literature data, our findings are consistent with the scenario that UCDs are the remnant nucleus of a stripped galaxy. We further investigate the discrepancy in the literature for M87's kinematics at large radii, favouring a declining velocity dispersion profile. This work has highlighted the need for more self-consistent studies of galaxy haloes.DAF thanks the ARC for financial support via DP160101608. AFM has received financial support through the Postdoctoral Junior Leader Fellowship Programme from “la Caixa” Banking Foundation (LCF/BQ/LI18/11630007). AJR was supported by National Science Foundation grant AST-1616710 and as a Research Corporation for Science Advancement Cottrell Scholar

Low-mass compact elliptical galaxies: Spatially resolved stellar populations and kinematics with the Keck Cosmic Web Imager

We present spatially resolved two-dimensional maps and radial trends of the stellar populations and kinematics for a sample of six compact elliptical galaxies (cE) using spectroscopy from the Keck Cosmic Web Imager (KCWI). We recover their star formation histories, finding that all except one of our cEs are old and metal rich, with both age and metallicity decreasing toward their outer radii. We also use the integrated values within one effective radius to study different scaling relations. Comparing our cEs with others from the literature and from simulations we reveal the formation channel that these galaxies might have followed. All our cEs are fast rotators, with relatively high rotation values given their low ellipticites. In general, the properties of our cEs are very similar to those seen in the cores of more massive galaxies, and in particular, to massive compact galaxies. Five out of our six cEs are the result of stripping a more massive (compact or extended) galaxy, and only one cE is compatible with having been formed intrinsically as the low-mass compact object that we see today. These results further confirm that cEs are a mixed-bag of galaxies that can be formed following different formation channels, reporting for the first time an evolutionary link within the realm of compact galaxies (at all stellar masses).AFM has received financial support through the Postdoctoral Junior Leader Fellowship Programme from ‘la Caixa’ Banking Foundation (LCF/BQ/LI18/11630007). AFM, DAF, and RM thank the ARC for financial support via DP160101608. AJR was supported by National Science Foundation grant AST-1616710 and as a Research Corporation for Science Advancement Cottrell Scholar. AA was supported in part by NASA program HST-GO-14747, contract NNG16PJ25C, and grant 80NSSC18K0563, and NSF award 1828315. RMcD is the recipient of an Australian Research Council Future Fellowship (project number FT150100333)

A NORMAL SUPERMASSIVE BLACK HOLE IN NGC. 1277

The identification of galaxies with "overly massive" black holes requires two measurements: a black hole mass (Mbh) and a host spheroid mass (${M}_{{\rm{sph,\ast }}}$). Here we provide our measurements for NGC 1277. Our structural decomposition reveals that NGC 1277 is dominated by a "classical" spheroid with a Sérsic index n = 5.3, a half-light radius ${R}_{{\rm{e,major}}}=2.1\;{\rm{kpc}}$, and a stellar mass of $2.7\times {10}^{11}\quad {M}_{\odot }$ (using ${M}_{*}/{L}_{V}=11.65$, Martín-Navarro et al.). This mass is an order of magnitude greater than originally reported. Using the latest Mbh–n, Mbh–${M}_{{\rm{sph,\ast }}}$, and Mbh–σ relations, the expected black hole mass is, respectively, (${0.57}_{-0.40}^{+1.29})\times {10}^{9}\quad {M}_{\odot }$, (${1.58}_{-1.13}^{+4.04})\times {10}^{9}\quad {M}_{\odot }$, and (${2.27}_{-1.44}^{+4.04})\times {10}^{9}\quad {M}_{\odot }$ (using σ = 300 km s−1) for which the "sphere-of-influence" is 0farcs31. Our new kinematical maps obtained from laser guide star assisted, adaptive optics on the Keck I Telescope dramatically reaffirm the presence of the inner, nearly edge-on, disk seen in the galaxy image. We also report that this produces a large velocity shear (~400 km s−1) across the inner 0farcs2 (70 pc) plus elevated values of $\sqrt{{\sigma }^{2}+{V}^{2}}$ across the inner (\pm 3\buildrel{\prime\prime}\over{.} 8)\times (\pm 0\buildrel{\prime\prime}\over{.} 6) region of the galaxy. Our new multi-Gaussian expansion (MGE) models and Jeans Anisotropic MGE analysis struggled to match this extended component. Our optimal black hole mass, albeit a probable upper limit because of the disk is 1.2 × 109 M⊙ ($M/{L}_{V}=12.3$). This is an order of magnitude smaller than originally reported and 4 times smaller than recently reported. It gives an ${M}_{{\rm{bh}}}/{M}_{{\rm{sph,\ast }}}$ ratio of 0.45% in agreement with the median (≈0.5%) and range (0.1%–5.0%) observed in non-dwarf, early-type galaxies. This result highlights the need for caution with inner disks