Keck spectroscopy of the faint dwarf elliptical galaxy population in the Perseus Cluster core: mixed stellar populations and a flat luminosity function

We present the result of a photometric and Keck-LRIS spectroscopic study of dwarf galaxies in the core of the Perseus Cluster, down to a magnitude of M_B = -12.5. Spectra were obtained for twenty-three dwarf-galaxy candidates, from which we measure radial velocities and stellar population characteristics from absorption line indices. From radial velocities obtained using these spectra we confirm twelve systems as cluster members, with the remaining eleven as non-members. Using these newly confirmed cluster members, we are able to extend the confirmed colour-magnitude relation for the Perseus Cluster down to M_B = -12.5. We confirm an increase in the scatter about the colour magnitude relationship below M_B = -15.5, but reject the hypothesis that very red dwarfs are cluster members. We measure the faint-end slope of the luminosity function between M_B = -18 and M_B = -12.5, finding alpha = -1.26 \pm 0.06, which is similar to that of the field. This implies that an overabundance of dwarf galaxies does not exist in the core of the Perseus Cluster. By comparing metal and Balmer absorption line indices with alpha-enhanced single stellar population models, we derive ages and metallicities for these newly confirmed cluster members. We find two distinct dwarf elliptical populations: an old, metal poor population with ages ~ 8 Gyr and metallicities [Fe/H] < -0.33, and a young, metal rich population with ages -0.33. Dwarf galaxies in the Perseus Cluster are therefore not a simple homogeneous population, but rather exhibit a range in age and metallicity.Comment: 12 pages, 9 figures. Accepted for publication in MNRA

Inter-agency adult support and protection practice:a realistic evaluation with police, health and social care professionals

Purpose: Collaborative inter-agency working is of paramount importance for the public protection agenda worldwide. The purpose of this paper is to disseminate the findings from a research study on the inter-agency working within adult support and protection (ASP) roles in the police, health and social care.Design/methodology/approach: This realistic evaluation study with two inter-related phases was funded by the Scottish Institute for Policing Research. This paper reports on Phase 1 which identified existing gaps in the implementation of effective inter-agency practice by reviewing the “state of play” in inter-agency collaboration between the police and health and social care professionals. In total, 13 focus groups comprising representatives from Police Scotland (n¼52), Social Care (n¼31) and Health (n¼18), engaged in single profession and mixed profession groups addressing issues including referral and information exchange.Findings: On analysing context-mechanism-outcome (CMO), gaps in joint working were identified and attributed to the professionals’ own understanding of inter-agency working and the expectations of partner agencies. It recommended the need for further research and inter-agency training on public protection. Research limitations/implications – This unique Scottish study successfully identified the inter-agency practices of health, social services and police. By means of a modified realistic evaluation approach, it provides an in-depth understanding of the challenges that professionals face on a day-to-day basis when safeguarding adults and informed strategic recommendations to overcome the barriers to good practices in organisational working. The methods used to determine CMO could benefit other researchers to develop studies exploring the complexities of multi-causal effects of cross-boundary working. The use of the same case study in each focus group helped to neutralise bias. However, the voluntary nature of participation could have resulted in biased perceptions. The limited numbers of health professionals may have resulted in less representation of health sector views.Practical implications: Collaborative inter-agency working is of paramount importance for public protection worldwide. This paper reports on a Scottish study that focussed on the coordinated and integrated practices amongst the police, health and social services’ professionals who support and protect adult members of society at risk of harm.Social implications: Whilst the focus of this study has been on ASP, the conclusions and recommendations are transferable to public protection issues in many other contexts.Originality/value: Studies on the joint-working practices amongst police and health and social services’ professionals who support and protect adult members of society at risk of harm are uncommon. This  study investigated professionals’ perceptions of gaps and concerns pertaining to integrated working by means of a realistic evaluation approach. It recommended the need for further research and inter-agency training on public protection

The many assembly histories of massive void galaxies as revealed by integral field spectroscopy

We present the first detailed integral field spectroscopy study of nine central void galaxies with M*>10¹⁰Mʘ using the Wide Field Spectrograph to determine how a range of assembly histories manifest themselves in the current day Universe.While the majority of these galaxies are evolving secularly, we find a range of morphologies, merger histories and stellar population distributions, though similarly low Hα-derived star formation rates (10¹⁰Mʘ have similarly low star formation rates

Dwarf galaxies in the Perseus Cluster: further evidence for a disc origin for dwarf ellipticals

We present the results of a Keck-ESI (Echellette Spectrograph and Imager) spectroscopic study of six dwarf elliptical (dE) galaxies in the Perseus Cluster core, and confirm two dwarfs as cluster members for the first time. All six dEs follow the size–magnitude relation for dE/dSph galaxies. Central velocity dispersions are measured for three Perseus dwarfs in our sample, and all lie on the σ–luminosity relation for early-type, pressure-supported systems. We furthermore examine SA 0426-002, a unique dE in our sample with a bar-like morphology surrounded by low surface brightness wings/lobes (μB = 27 mag arcsec¯²). Given its morphology, velocity dispersion (σ₀ = 33.9 ± 6.1 km s⁻¹), velocity relative to the brightest cluster galaxy NGC 1275 (2711 km s⁻¹), size (Rₑ = 2.1 ± 0.10 kpc), and Sersic index ( ´ n = 1.2 ± 0.02), we hypothesize the dwarf has morphologically transformed from a low-mass disc to dE via harassment. The low surface brightness lobes can be explained as a ring feature, with the bar formation triggered by tidal interactions via speed encounters with Perseus Cluster members. Alongside spiral structure found in dEs in Fornax and Virgo, SA 0426-002 provides crucial evidence that a fraction of bright dEs have a disc infall origin, and are not part of the primordial cluster population

Black hole scaling relations of active and quiescent galaxies: Addressing selection effects and constraining virial factors

Local samples of quiescent galaxies with dynamically measured black hole masses (Mbh) may suffer from an angular resolution-related selection effect, which could bias the observed scaling relations between Mbh and host galaxy properties away from the intrinsic relations. In particular, previous work has shown that the observed Mbh-Mstar (stellar mass) relation is more strongly biased than the Mbh-sigma (velocity dispersion) relation. Local samples of active galactic nuclei (AGN) do not suffer from this selection effect, as in these samples Mbh is estimated from megamasers and/or reverberation mapping-based techniques. With the exception of megamasers, Mbh-estimates in these AGN samples are proportional to a virial coefficient fvir. Direct modelling of the broad line region suggests that fvir~3.5. However, this results in a Mbh-Mstar relation for AGN which lies below and is steeper than the one observed for quiescent black hole samples. A similar though milder trend is seen for the Mbh-sigma relation. Matching the high-mass end of the Mbh-Mstar and Mbh-sigma relations observed in quiescent samples requires fvir~15 and fvir~7, respectively. On the other hand, fvir~3.5 yields Mbh-sigma and Mbh-Mstar relations for AGN which are remarkably consistent with the expected `intrinsic' correlations for quiescent samples (i.e., once account has been made of the angular resolution-related selection effect), providing additional evidence that the sample of local quiescent black holes is biased. We also show that, as is the case for quiescent black holes, the Mbh-Mstar scaling relation of AGN is driven by velocity dispersion, thus providing additional key constraints to black hole-galaxy co-evolution models.Comment: 15 pages, 5 Figures. MNRAS, accepte

Tidal interactions at the edge of the Local Group: New evidence for tidal features in the Antlia Dwarf Galaxy

Using deep B band imaging down to mu_{B} = 26 mag arcsec^{-2}, we present evidence for tidal tails in the Antlia Dwarf galaxy, one of the most distant members of the Local Group. This elongation is in the direction of Antlia's nearest neighbor, the Magellanic-type NGC 3109. The tail is offset by less than 10 degrees from a vector linking the centers of the two galaxies, indicative of interactions between the pair. Combined with the warped disc previously identified in NGC 3109, Antlia and NGC 3109 must be at a small separation for tidal features to be present in Antlia. We calculate that Antlia cannot be completely disrupted by NGC 3109 in a single interaction unless its orbit pericenter is less than 6 kpc, however multiple interactions could significantly alter its morphology. Therefore despite being located right at the edge of the Local Group, environmental effects are playing an important role in Antlia's evolution.Comment: 8 pages, 4 figures, accepted for publication in ApJ

Ultracompact dwarfs in the Perseus Cluster:UCD formation via tidal stripping

We present the results of a Keck/DEIMOS survey of Ultra Compact Dwarfs (UCDs) in the Perseus Cluster core. We confirm cluster membership for 14 UCDs, with radial velocities ~5300 km s$^{-1}$. Two of these confirmed Perseus UCDs have extremely blue colours ($B-R < 0.6$ mag), reside in star forming filaments surrounding NGC 1275, and have likely formed as massive star clusters in the last ~100 Myr. We also measure a central velocity dispersion of a third, UCD13 ($\sigma_0 = 38 \pm 8$ km s$^{-1}$), the most extended UCD in our sample. We determine it to have radius $R_{e} = 85 \pm 1.1$ pc, a dynamical mass of ($2.3 \pm 0.8)\times10^{8}$ M$_{\odot}$, and a metallicity [Z/H]$= -0.52^{+0.33}_{-0.29}$ dex. UCD13 and the cluster's central galaxy, NGC 1275, have a projected separation of 30 kpc and a radial velocity difference of ~20 km s$^{-1}$. Based on its size, red colour, internal velocity dispersion, dynamical mass, metallicity and proximity to NGC 1275, we argue that UCD13 is likely the remnant nucleus of a tidally stripped dE, with this progenitor dE having $M_{B} \approx -16$ mag and mass $\sim10^{9}$ M$_{\odot}$.Comment: 9 pages, 5 figures, accepted for publication in MNRA

Hubble Space Telescope survey of the Perseus Cluster -IV: Compact stellar systems in the Perseus Cluster core and Ultra Compact Dwarf formation in star forming filaments

We present the results of the first search for Ultra Compact Dwarfs (UCDs) in the Perseus Cluster core, including the region of the cluster around the unusual Brightest Cluster Galaxy (BCG) NGC 1275. Utilising Hubble Space Telescope Advanced Camera for Surveys imaging, we identify a sample of 84 UCD candidates with half-light radii 10 pc < r_e < 57 pc out to a distance of 250 kpc from the cluster centre, covering a total survey area of ~70 armin^2. All UCDs in Perseus lie in the same size-luminosity locus seen for confirmed UCDs in other regions of the local Universe. The majority of UCDs are brighter than M_R = -10.5, and lie on an extrapolation of the red sequence followed by the Perseus Cluster dwarf elliptical population to fainter magnitudes. However, three UCD candidates in the vicinity of NGC 1275 are very blue, with colours (B-R)_0 < 0.6 implying a cessation of star formation within the past 100 Myr. Furthermore, large blue star clusters embedded in the star forming filaments are highly indicative that both proto-globular clusters (GCs) and proto-UCDs are actively forming at the present day in Perseus. We therefore suggest star forming filaments as a formation site for some UCDs, with searches necessary in other low redshift analogues of NGC 1275 necessary to test this hypothesis. We also suggest that tidal disruption of dwarf galaxies is another formation channel for UCD formation in the core of Perseus as tidal disruption is ongoing in this region as evidenced by shells around NGC 1275. Finally, UCDs may simply be massive GCs based on strong similarities in the colour trends of the two populations.Comment: 18 pages, 20 figures, 3 tables. Accepted for publication in MNRA

A population of faint low surface brightness galaxies in the Perseus cluster core

We present the detection of 89 low surface brightness (LSB), and thus low stellar density galaxy candidates in the Perseus cluster core, of the kind named ‘ultra-diffuse galaxies’, with mean effective V-band surface brightnesses 24.8-27.1 mag arcsec−2, total V-band magnitudes −11.8 to −15.5 mag, and half-light radii 0.7-4.1 kpc. The candidates have been identified in a deep mosaic covering 0.3 square degrees, based on wide-field imaging data obtained with the William Herschel Telescope. We find that the LSB galaxy population is depleted in the cluster centre and only very few LSB candidates have half-light radii larger than 3 kpc. This appears consistent with an estimate of their tidal radius, which does not reach beyond the stellar extent even if we assume a high dark matter content (M/L = 100). In fact, three of our candidates seem to be associated with tidal streams, which points to their current disruption. Given that published data on faint LSB candidates in the Coma cluster – with its comparable central density to Perseus – show the same dearth of large objects in the core region, we conclude that these cannot survive the strong tides in the centres of massive clusters