Globular clusters in the stellar stream surrounding the Milky Way analog NGC 5907

We study the globular clusters (GCs) in the spiral galaxy NGC~5907 well-known for its spectacular stellar stream -- to better understand its origin. Using wide-field Subaru/Suprime-Cam $gri$ images and deep Keck/DEIMOS multi-object spectroscopy, we identify and obtain the kinematics of several GCs superimposed on the stellar stream and the galaxy disk. We estimate the total number of globular clusters in NGC 5907 to be $154\pm44$, with a specific frequency of $0.73\pm0.21$. Our analysis also reveals a significant, new population of young star cluster candidates found mostly along the outskirts of the stellar disk. Using the properties of the stream GCs, we estimate that the disrupted galaxy has a stellar mass similar to the Sagittarius dwarf galaxy accreted by the Milky Way, i.e. $\sim10^8~M_\odot$.Comment: 9 pages, 9 figures, catalog of GCs is available in online versio

Globular clusters in the stellar stream surrounding the Milky Way analogue NGC 5907

We study the globular clusters (GCs) in the spiral galaxy NGC 5907 well-known for its spectacular stellar stream-to better understand its origin. Using wide-field Subaru/Suprime-Cam gri images and deep Keck/DEIMOS multi-object spectroscopy, we identify and obtain the kinematics of several GCs superimposed on the stellar stream and the galaxy disc. We estimate the total number of GCs in NGC 5907 to be 154 ± 44, with a specific frequency of 0.73 ± 0.21. Our analysis also reveals a significant, new population of young star cluster candidates found mostly along the outskirts of the stellar disc. Using the properties of the stream GCs, we estimate that the disrupted galaxy has a stellar mass similar to the Sagittarius dwarf galaxy accreted by the Milky Way, i.e

An expanded catalogue of low surface brightness galaxies in the Coma cluster using Subaru/Suprime-Cam

We present a catalogue of low surface brightness (LSB) galaxies in the Coma cluster obtained from deep Subaru/Suprime-Cam V and R-band imaging data within a region of $\sim$4 deg$^2$. We increase the number of LSB galaxies presented in Yagi et al. (2016) by a factor of $\sim$3 and report the discovery of 29 new ultra-diffuse galaxies (UDGs). We compile the largest sample of ultra-diffuse galaxies with colours and structural parameters in the Coma cluster. While most UDGs lie along the red-sequence relation of the colour-magnitude diagram, $\sim$5per cent are outside (bluer or redder) the red-sequence region of Coma cluster galaxies. Our analyses show that there is no special distinction in the basic photometric parameters between UDGs and other LSB galaxies. We investigate the clustercentric colour distribution and find a remarkable transition at a projected radius of $\sim$0.6 Mpc. Within this cluster core region, LSB galaxies are, on average, redder than co-spatial higher surface brightness galaxies, highlighting how vulnerable LSB galaxies are to the physical processes at play in the dense central region of the cluster. The position of the transition radius agrees with expectations from recent cosmological simulation of massive galaxy clusters within which ancient infalls are predicted to dominate the LSB galaxy population.Comment: Accepted for publication in MNRAS. The complete version of Table 2 is available online as supplementary materia

An expanded catalogue of low surface brightness galaxies in the Coma cluster using Subaru/Suprime-Cam

We present a catalogue of low surface brightness (LSB) galaxies in the Coma cluster obtained from deep Subaru/Suprime-Cam V- and R-band imaging data within a region of -4 deg2. We increase the number of LSB galaxies presented in Yagi et al. (2016) by a factor of -3 and report the discovery of 29 new ultradiffuse galaxies (UDGs). We compile the largest sample of UDGs with colours and structural parameters in the Coma cluster. While most UDGs lie along the red-sequence relation of the colour–magnitude diagram, -16 per cent are outside (bluer or redder) the red-sequence region of Coma cluster galaxies. Our analyses show that there is no special distinction in the basic photometric parameters between UDGs and other LSB galaxies. We investigate the clustercentric colour distribution and find a remarkable transition at a projected radius of -0.6 Mpc. Within this cluster core region and relative to the red-sequence of galaxies, LSB galaxies are on average redder than co-spatial higher surface brightness galaxies at the 2σ level, highlighting how vulnerable LSB galaxies are to the physical processes at play in the dense central region of the cluster. The position of the transition radius agrees with expectations from recent cosmological simulation of massive galaxy clusters within which ancient infalls are predicted to dominate the LSB galaxy population

NGC 474 as viewed with KCWI: Diagnosing a shell galaxy

We present new spectra obtained using Keck/KCWI and perform kinematics and stellar population analyses of the shell galaxy NGC 474, from both the galaxy centre and a region from the outer shell. We show that both regions have similarly extended star formation histories although with different stellar population properties. The central region of NGC 474 is dominated by intermediate-Aged stars (8.3 ± 0.3 Gyr) with subsolar metallicity ([Z/H] =-0.24 ± 0.07 dex) while the observed shell region, which hosts a substantial population of younger stars, has a mean luminosity-weighted age of 4.0 ± 0.5 Gyr with solar metallicities ([Z/H] =-0.03 ± 0.09 dex). Our results are consistent with a scenario in which NGC 474 experienced a major to intermediate merger with a log$(M_∗/\rm M_\odot) \sim 10$ mass satellite galaxy at least ${\sim}2$ Gyr ago which produced its shell system. This work shows that the direct spectroscopic study of low-surface brightness stellar features, such as shells, is now feasible and opens up a new window to understanding galaxy formation and evolution

NGC 474 as viewed with KCWI: diagnosing a shell galaxy

We present new spectra obtained using Keck/KCWI and perform kinematics and stellar population analyses of the shell galaxy NGC 474, from both the galaxy centre and a region from the outer shell. We show that both regions have similarly extended star formation histories although with different stellar population properties. The central region of NGC 474 is dominated by intermediate-aged stars (8.3 \pm 0.3 Gyr) with subsolar metallicity ([Z/H]= -0.24 \pm 0.07 dex) while the observed shell region, which hosts a substantial population of younger stars, has a mean luminosity-weighted age of 4.0 \pm 0.5 Gyr with solar metallicities ([Z/H]=-0.03 \pm 0.09 dex). Our results are consistent with a scenario in which NGC 474 experienced a major to intermediate merger with a log$(M_*/M_\odot)\sim10$ mass satellite galaxy at least \sim 2 Gyr ago which produced its shell system. This work shows that the direct spectroscopic study of low-surface brightness stellar features, such as shells, is now feasible and opens up a new window to understanding galaxy formation and evolution.Comment: Accepted for publication in MNRAS, 6 pages, 5 figure

The SLUGGS survey: chromodynamical modelling of the lenticular galaxy NGC 1023

Globular clusters (GCs) can be considered discrete, long-lived, dynamical tracers that retain crucial information about the assembly history of their parent galaxy. In this paper, we present a new catalogue of GC velocities and colours for the lenticular galaxy NGC 1023, we study their kinematics and spatial distribution, in comparison with the underlying stellar kinematics and surface brightness profile, and we test a new method for studying GC properties. Specifically, we decompose the galaxy light into its spheroid (assumed to represent the bulge+halo components) and disc components and use it to assign to each GC a probability of belonging to one of the two components. Then we model the galaxy kinematics, assuming a disc and spheroidal component, using planetary nebulae and integrated stellar light. We use this kinematic model and the probability previously obtained from the photometry to recalculate for each GC its likelihood of being associated with the disc, the spheroid, or neither. We find that the reddest GCs are likely to be associated with the disc, as found for faint fuzzies in this same galaxy, suggesting that the disc of this S0 galaxy originated at z ≃ 2. The majority of blue GCs are found likely to be associated with the spheroidal (hot) component. The method also allows us to identify objects that are unlikely to be in equilibrium with the system. In NGC 1023 some of the rejected GCs form a substructure in phase space that is connected with NGC 1023 companion galaxy

Chromodynamical analysis of lenticular galaxies using globular clusters and planetary nebulae

Recovering the origins of lenticular galaxies can shed light on the understanding of galaxy formation and evolution, since they present properties that can be found in both elliptical and spiral galaxies. In this work we study the kinematics of the globular cluster (GC) systems of three lenticular galaxies located in low density environments (NGC2768, NGC3115 and NGC7457), and compare them with the kinematics of planetary nebulae (PNe). The PNe and GC data come from the Planetary Nebulae Spectrograph and the SLUGGS Surveys. Through photometric spheroid-disc decomposition and PNe kinematics we find the probability for a given GC to belong to either the spheroid or the disc of its host galaxy or be rejected from the model. We find that there is no correlation between the components that the GCs are likely to belong to and their colours. Particularly, for NGC2768 we find that its red GCs display rotation preferentially at inner radii (Re < 1). In the case of the GC system of NGC3115 we find a group of GCs with similar kinematics that are not likely to belong to neither its spheroid nor disc. For NGC7457 we find that 70% of its GCs are likely to belong to the disc. Overall, our results suggest that these galaxies assembled into S0s through different evolutionary paths. Mergers seem to have been very important for NGC2768 and NGC3115 while NGC7457 is more likely to have experienced secular evolution

NGC 474 as viewed with KCWI: Diagnosing a shell galaxy

We present new spectra obtained using Keck/KCWI and perform kinematics and stellar population analyses of the shell galaxy NGC 474, from both the galaxy centre and a region from the outer shell. We show that both regions have similarly extended star formation histories although with different stellar population properties. The central region of NGC 474 is dominated by intermediate-Aged stars (8.3 ± 0.3 Gyr) with subsolar metallicity ([Z/H] =-0.24 ± 0.07 dex) while the observed shell region, which hosts a substantial population of younger stars, has a mean luminosity-weighted age of 4.0 ± 0.5 Gyr with solar metallicities ([Z/H] =-0.03 ± 0.09 dex). Our results are consistent with a scenario in which NGC 474 experienced a major to intermediate merger with a log$(M_∗/\rm M_\odot) \sim 10$ mass satellite galaxy at least ${\sim}2$ Gyr ago which produced its shell system. This work shows that the direct spectroscopic study of low-surface brightness stellar features, such as shells, is now feasible and opens up a new window to understanding galaxy formation and evolution.AFM acknowledges financial support from LCF/BQ/LI18/11630007. AJR was supported by National Science Foundation grant AST-1616710 and as a Research Corporation for Science Advancement Cottrell Scholar. DAF thanks the ARC for financial support via DP160101608. ABA and JPB gratefully acknowledge support from National Science foundation grants AST- 1518294 and AST-1616598

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)