We aim to explore the relationship between globular cluster total number, $N_{\rm GC}$, and central black hole mass, $M_\bullet$, in spiral galaxies, and compare it with that recently reported for ellipticals. We present results for the Sbc galaxy NGC 4258, from Canada France Hawaii Telescope data. Thanks to water masers with Keplerian rotation in a circumnuclear disk, NGC 4258 has the most precisely measured extragalactic distance and supermassive black hole mass to date. The globular cluster (GC) candidate selection is based on the ($u^*\ -\ i^\prime$) vs. ($i^\prime\ -\ K_s$) diagram, which is a superb tool to distinguish GCs from foreground stars, background galaxies, and young stellar clusters, and hence can provide the best number counts of GCs from photometry alone, virtually free of contamination, even if the galaxy is not completely edge-on. The mean optical and optical-near infrared colors of the clusters are consistent with those of the Milky Way and M 31, after extinction is taken into account. We directly identify 39 GC candidates; after completeness correction, GC luminosity function extrapolation and correction for spatial coverage, we calculate a total $N_{\rm GC} = 144\pm31^{+38}_{-36}$ (random and systematic uncertainties, respectively). We have thus increased to 6 the sample of spiral galaxies with measurements of both $M_\bullet$ and $N_{\rm GC}$. NGC 4258 has a specific frequency $S_{\rm N} = 0.4\pm0.1$ (random uncertainty), and is consistent within 2$\sigma$ with the $N_{\rm GC}$ vs. $M_\bullet$ correlation followed by elliptical galaxies. The Milky Way continues to be the only spiral that deviates significantly from the relation.
We report the photometric properties of 16 dwarf galaxies, 15 of which are newly identified, in the Western halo of the nearby giant elliptical galaxy NGC5128. All candidates are found at projected distances $\sim\!100\!-\!225$kpc from their giant host, with luminosities $-10.82\!\leq\!M_V/{\rm mag}\!\leq\!-7.42$ and effective radii $4''\!\leq\!r_{\rm eff}\!\leq\!17''$ (or $75\!\leq\!r_{\rm eff}/{\rm pc}\!\leq\!300$ at the distance of NGC5128). We compare to other low-mass dwarf galaxies in the local universe and find them to populate the faint/compact extension of the size-luminosity relation that was previously not well-sampled by dwarf galaxies in the Centaurus A system, with optical colors similar to compact stellar systems like globular clusters and ultra-compact dwarf galaxies despite having much more diffuse morphologies. From optical $u'g'r'i'z'$ photometry, stellar masses are estimated to be $5.17\!\leq\!\log{\cal M}_\star/M_\odot\!\leq\!6.48$, with colors that show them to fall redward of the dwarf galaxy mass-metallicity relation. These colors suggest star formation histories that require some mechanism that would give rise to extra metal enrichment such as primordial formation within the halos of their giant galaxy hosts, non-primordial star formation from previously enriched gas, or extended periods of star formation leading to self-enrichment. We also report the existence of at least two sub-groups of dwarf candidates, each subtending $10-20'$ on the sky, corresponding to projected physical separations of $10\!-\!20$kpc. True physical associations of these groups, combined with their potentially extended star formation histories, would imply that they may represent dwarf galaxy groups in the early stage of interaction upon infall into a giant elliptical galaxy halo in the very nearby universe.
ABSTRACT We present our study of 19 low X-ray luminosity galaxy clusters ( L X∼ 0.5–45 × 10 43 erg s −1 ), selected from the ROSAT Position Sensitive Proportional Counters Pointed Observations and the revised version of Mullis et al. in the redshift range of 0.16–0.7. This is the introductory paper of a series presenting the sample selection, photometric and spectroscopic observations, and data reduction. Photometric data in different passbands were taken for eight galaxy clusters at Las Campanas Observatory; three clusters at Cerro Tololo Interamerican Observatory; and eight clusters at the Gemini Observatory. Spectroscopic data were collected for only four galaxy clusters using Gemini telescopes. Using the photometry, the galaxies were defined based on the star-galaxy separation taking into account photometric parameters. For each galaxy cluster, the catalogs contain the point-spread function and aperture magnitudes of galaxies within the 90% completeness limit. They are used together with structural parameters to study the galaxy morphology and to estimate photometric redshifts. With the spectroscopy, the derived galaxy velocity dispersion of our clusters ranged from 507 km s −1 for [VMF98]022 to 775 km s −1 for [VMF98]097 with signs of substructure. Cluster membership has been extensively discussed taking into account spectroscopic and photometric redshift estimates. In this sense, members are the galaxies within a projected radius of 0.75 Mpc from the X-ray emission peak and with clustercentric velocities smaller than the cluster velocity dispersion or 6000 km s −1 , respectively. These results will be used in forthcoming papers to study, among the main topics, the red cluster sequence, blue cloud and green populations, the galaxy luminosity function, and cluster dynamics.
We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded $u, g$ and $i$-band image obtained with the DECam wide-field camera mounted on the 4-meter Blanco telescope at the Cerro Tololo Interamerican Observatory as part of the {\it Next Generation Fornax Survey} (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii $0.1\!<\!r_e\!<\!2.8$ kpc and average effective surface brightness values $22.0\!<\!\mu_i\!<\!28.0$ mag arcsec$^{-2}$. We confirm the existence of ultra-diffuse galaxies (UDGs) in the Fornax core regions that resemble counterparts recently discovered in the Virgo and Coma galaxy clusters.~We also find extremely low surface brightness NGFS dwarfs, which are several magnitudes fainter than the classical UDGs. The faintest dwarf candidate in our NGFS sample has an absolute magnitude of $M_i\!=\!-8.0$\,mag. The nucleation fraction of the NGFS dwarf galaxy sample appears to decrease as a function of their total luminosity, reaching from a nucleation fraction of $>\!75\%$ at luminosities brighter than $M_i\!\simeq\!-15.0$ mag to $0\%$ at luminosities fainter than $M_i\!\simeq\!-10.0$ mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below $\sim\!100$ kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.
We continue to explore the relationship between globular cluster total number, $N_{\rm GC}$, and central black hole mass, $M_\bullet$, in spiral galaxies. We present here results for the Sab galaxies NGC 3368, NGC 4736 (M 94) and NGC 4826 (M 64), and the Sm galaxy NGC 4395. The globular cluster (GC) candidate selection is based on the ($u^*$ - $i^\prime$) versus ($i^\prime$ - $K_s$) color-color diagram, and $i^\prime$-band shape parameters. We determine the $M_\bullet$ versus $N_{\rm GC}$ correlation for these spirals, plus NGC 4258, NGC 253, M 104, M 81, M 31, and the Milky Way. We also redetermine the correlation for the elliptical sample in Harris, Poole, & Harris (2014), with updated galaxy types from Sahu et al. 2019b. Additionally, we derive total stellar galaxy mass, $M_\ast$, from its two-slope correlation with $N_{\rm GC}$ (Hudson, Harris, & Harris 2014), and fit $M_\bullet$ versus $M_\ast$ for both spirals and ellipticals. We obtain log $M_\bullet \propto$ (1.01 $\pm$ 0.13) log $N_{\rm GC}$ for ellipticals, and log $M_\bullet \propto$ (1.64 $\pm$ 0.24) log $N_{\rm GC}$ for late type galaxies (LTG). The linear $M_\bullet$ versus $N_{\rm GC}$ correlation in ellipticals could be due to statistical convergence through mergers, but not the much steeper correlation for LTG. However, in the $M_\bullet$ versus total stellar mass ($M_\ast$) parameter space, with $M_\ast$ derived from its correlation with $N_{\rm GC}$, $M_\bullet \propto$ (1.48 $\pm$ 0.18) log $M_\ast$ for ellipticals, and $M_\bullet \propto$ (1.21 $\pm$ 0.16) log $M_\ast$ for LTG. The observed agreement between ellipticals and LTG in this parameter space may imply that black holes and galaxies co-evolve through "calm" accretion, AGN feedback, and other secular processes.
ABSTRACT Many processes have been proposed to explain the quenching of star formation in spiral galaxies and their transformation into S0s. These processes affect the bulge and disc in different ways, and so by isolating the bulge and disc spectra, we can look for these characteristic signatures. In this work, we used buddi to cleanly extract the spectra of the bulges and discs of 78 S0 galaxies in the MaNGA Survey. We compared the luminosity and mass weighted stellar populations of the bulges and discs, finding that bulges are generally older and more metal rich than their discs. When considering the mass and environment of each galaxy, we found that the galaxy stellar mass plays a more significant role on the formation of the bulges. Bulges in galaxies with masses $\ge 10^{10}\, {\rm M}_\odot$ built up the majority of their mass rapidly early in their lifetimes, while those in lower mass galaxies formed over more extended time-scales and more recently. No clear difference was found in the formation or quenching processes of the discs as a function of galaxy environment. We conclude that more massive S0 galaxies formed through an inside-out scenario, where the bulge formed first and evolved passively while the disc underwent a more extended period of star formation. In lower mass S0s, the bulges and discs either formed together from the same material, or through an outside-in scenario. Our results therefore imply multiple formation mechanisms for S0 galaxies, the pathway of which is chiefly determined by a galaxy’s current stellar mass.
Abstract All satellite galaxies experience environmental secular evolution as they are accreted onto their host systems. Observations and simulations indicate that the closer they are to their hosts, the higher their dark matter densities are. Using the NGFS deep photometric observations of 630 satellites in the Fornax galaxy cluster we discover that their mean stellar densities also show such anti-correlation with their distances to the cluster center, correlating with the host tidal density field, up to a transition radius at ℜ ★ ≈ 0.4𝑹 vir (400 kpc), beyond which the stellar densities increase again. Comparisons with satellites of a Fornax-type cluster in the TNG50 simulation reveal a similar break at ℜ ★ ≈ 0.5𝑹 vir in deprojection, while their mean dark matter densities keep decreasing with distance to their host. Moreover, the relative fraction of gas-rich satellites and gaseous densities decrease significantly within ℜ ★ . We expand our analysis to satellites in different environments probing the more massive Virgo cluster, and also the less massive Milky Way and Andromeda systems, finding a similar behavior and transition radius in units of 𝑹 vir for each system of satellites, with ℜ ★ ∼ 0.4 − 0.6𝑹 vir . This transition radius, if universal, could provide a useful observational diagnostic tool to identify the regions where the cluster environment would have processed the baryonic component of the accreted satellites more strongly, and where the more pristine population would be located. Finally, we suggest the utility of calibrating ℜ ★ as a possible photometric virial mass estimator.
We continue to explore the relationship between globular cluster total number, $N_{\rm GC}$, and central black hole mass, $M_\bullet$, in spiral galaxies. We present here results for the Sab galaxies NGC 3368, NGC 4736 (M 94) and NGC 4826 (M 64), and the Sm galaxy NGC 4395. The globular cluster (GC) candidate selection is based on the ($u^*$ - $i^\prime$) versus ($i^\prime$ - $K_s$) color-color diagram, and $i^\prime$-band shape parameters. We determine the $M_\bullet$ versus $N_{\rm GC}$ correlation for these spirals, plus NGC 4258, NGC 253, M 104, M 81, M 31, and the Milky Way. We also redetermine the correlation for the elliptical sample in Harris, Poole, & Harris (2014), with updated galaxy types from Sahu et al. 2019b. Additionally, we derive total stellar galaxy mass, $M_\ast$, from its two-slope correlation with $N_{\rm GC}$ (Hudson, Harris, & Harris 2014), and fit $M_\bullet$ versus $M_\ast$ for both spirals and ellipticals. We obtain log $M_\bullet \propto$ (1.01 $\pm$ 0.13) log $N_{\rm GC}$ for ellipticals, and log $M_\bullet \propto$ (1.64 $\pm$ 0.24) log $N_{\rm GC}$ for late type galaxies (LTG). The linear $M_\bullet$ versus $N_{\rm GC}$ correlation in ellipticals could be due to statistical convergence through mergers, but not the much steeper correlation for LTG. However, in the $M_\bullet$ versus total stellar mass ($M_\ast$) parameter space, with $M_\ast$ derived from its correlation with $N_{\rm GC}$, $M_\bullet \propto$ (1.48 $\pm$ 0.18) log $M_\ast$ for ellipticals, and $M_\bullet \propto$ (1.21 $\pm$ 0.16) log $M_\ast$ for LTG. The observed agreement between ellipticals and LTG in this parameter space may imply that black holes and galaxies co-evolve through "calm" accretion, AGN feedback, and other secular processes.
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