External Galaxies Commons^™

Discovery Of An Ultra-Diffuse Galaxy In The Pisces-Perseus Supercluster, David Martínez-Delgado, Ronald Läsker, Margarita Sharina, Elisa Toloba, Jürgen Fliri, Rachael Beaton, David Valls-Gabaud, Igor Karachentsev, Taylor Chonis, Eva Grebel, Duncan Forbes, Aaron Romanowsky, J. Gallego-Laborda, Karel Teuwen, M. Gómez-Flechoso, Jie Wang, Puragra Guhathakurta, Serafim Kaisin, Nhung Ho

Faculty Publications

We report the discovery of DGSAT I, an ultra-diffuse, quenched galaxy located 10fdg4 in projection from the Andromeda galaxy (M31). This low-surface brightness galaxy (μV = 24.8 mag arcsec−2), found with a small amateur telescope, appears unresolved in sub-arcsecond archival Subaru/Suprime-Cam images, and hence has been missed by optical surveys relying on resolved star counts, in spite of its relatively large effective radius (Re(V) = 12'') and proximity (15') to the well-known dwarf spheroidal galaxy And II. Its red color (V − I = 1.0), shallow Sérsic index (nV = 0.68), and the absence of detectable Hα emission are typical …

An Overmassive Dark Halo Around An Ultra-Diffuse Galaxy In The Virgo Cluster, Michael Beasley, Aaron Romanowsky, Vincenzo Pota, Ignacio Navarro, David Martinez-Delgado, Fabian Neyer, Aaron Deich

Faculty Publications

No abstract provided.

Stellar Populations Across The Black Hole Mass–Velocity Dispersion Relation, Ignacio Martín-Navarro, Jean Brodie, Remco Van Den Bosch, Aaron Romanowsky, Duncan Forbes

Faculty Publications

Coevolution between supermassive black holes (BH) and their host galaxies is universally adopted in models for galaxy formation. In the absence of feedback from active galactic nuclei (AGNs), simulated massive galaxies keep forming stars in the local universe. From an observational point of view, however, such coevolution remains unclear. We present a stellar population analysis of galaxies with direct BH mass measurements and the BH mass–σ relation as a working framework. We find that over-massive BH galaxies, i.e., galaxies lying above the best-fitting BH mass–σ line, tend to be older and more α-element-enhanced than under-massive BH galaxies. The scatter in …

A High Stellar Velocity Dispersion And ~100 Globular Clusters For The Ultra-Diffuse Galaxy Dragonfly 44, Pieter Van Dokkum, Roberto Abraham, Jean Brodie, Charlie Conroy, Shany Danieli, Allison Merritt, Lamiya Mowla, Aaron Romanowsky, Jielai Zhang

Faculty Publications

No abstract provided.

The Sluggs Survey: Inferring The Formation Epochs Of Metal-Poor And Metal-Rich Globular Clusters, Duncan Forbes, Nicola Pastorello, Aaron Romanowsky, Christopher Usher, Jean Brodie, Jay Strader

Faculty Publications

We present a novel, observationally-based framework for the formation epochs and sites of globular clusters (GCs) in a cosmological context. Measuring directly the mean ages of the metal-poor and metal-rich GC subpopulations in our own Galaxy, and in other galaxies, is observationally challenging. Here we apply an alternative approach utilizing the property that the galaxy mass–metallicity relation is a strong function of redshift (or look-back age) but is relatively insensitive to galaxy mass for massive galaxies. Assuming that GCs follow galaxy mass–metallicity relations that evolve with redshift, one can estimate the mean formation epochs of the two GC subpopulations by …

Vimos Mosaic Integral-Field Spectroscopy Of The Bulge And Disc Of The Early-Type Galaxy Ngc 4697, C. Spiniello, N. Napolitano, L. Coccato, V. Pota, Aaron Romanowsky, C. Tortora, G. Covone, M. Capaccioli

Faculty Publications

No abstract provided.

The Sluggs Survey: Globular Cluster Kinematics In A ‘Double Sigma’ Galaxy – Ngc 4473, Adebusola Alabi, Caroline Foster, Duncan Forbes, Aaron Romanowsky, Nicola Pastorello, Jean Brodie, Lee Spitler, Jay Strader, Christopher Usher

Faculty Publications

NGC 4473 is a so-called double sigma (2σ) galaxy, i.e. a galaxy with rare, double peaks in its 2D stellar velocity dispersion. Here, we present the globular cluster (GC) kinematics in NGC 4473 out to ∼10Re (effective radii) using data from combined Hubble Space Telescope/Advanced Camera for Surveys and Subaru/Suprime-Cam imaging and Keck/Deep Imaging Multi-Object Spectrograph. We find that the 2σ nature of NGC 4473 persists up to 3Re, though it becomes misaligned to the photometric major axis. We also observe a significant offset between the stellar and GC rotation amplitudes. This offset can be understood as a co-addition of …

The Sluggs Survey: Combining Stellar And Globular Cluster Metallicities In The Outer Regions Of Early-Type Galaxies, Nicola Pastorello, Duncan Forbes, Christopher Usher, Jean Brodie, Aaron Romanowsky, Jay Strader, Lee Spitler, Adebusola Alabi, Caroline Foster, Zachary Jennings, Sreeja Kartha, Vincenzo Pota

Faculty Publications

The outer halo regions of early-type galaxies carry key information about their past accretion history. However, spectroscopically probing the stellar component at such galactocentric radii is still challenging. Using the DEep Imaging Multi-Object Spectrograph on the Keck, we have been able to measure the metallicities of the stellar and globular cluster components in 12 early-type galaxies out to more than 10Re. We find similar metallicity gradients for the metal-poor and metal-rich globular cluster subpopulations, suggesting a common formation process for the two subpopulations. This is in conflict with most current theoretical predictions, where the metal-poor globular clusters are thought to …

The Sluggs Survey: Multipopulation Dynamical Modelling Of The Elliptical Galaxy Ngc 1407 From Stars And Globular Clusters, Vincenzo Pota, Aaron Romanowsky, Jean Brodie, Jorge Peñarrubia, Duncan Forbes, Nicola Napolitano, Caroline Foster, Matthew Walker, Jay Strader, Joel Roediger

Faculty Publications

No abstract provided.

Spectroscopic Confirmation Of The Existence Of Large, Diffuse Galaxies In The Coma Cluster, Pieter Van Dokkum, Aaron Romanowsky, Roberto Abraham, Jean Brodie, Charlie Conroy, Marla Geha, Allison Merritt, Alexa Villaume, Jielai Zhang

Faculty Publications

No abstract provided.

A Search For Young Stars In The S0 Galaxies Of A Super-Group At Z=0.37, Dennis W. Just, Dennis Zaritsky, Kim-Vy H. Tran, Anthony H. Gonzalez, Stefan Kautsch, John Moustakas

Chemistry and Physics Faculty Articles

We analyze Galaxy Evolution Explorer UV data for a system of four gravitationally bound groups at z = 0.37, SG1120, which is destined to merge into a Coma-mass cluster by z = 0, to study how galaxy properties may change during cluster assembly. Of the 38 visually classified S0 galaxies, with masses ranging from log (M *)[M ☉] ≈ 10-11, we detect only one in the near-UV (NUV) channel, a strongly star-forming S0 that is the brightest UV source with a measured redshift placing it in SG1120. Stacking the undetected S0 galaxies (which generally lie on or near …

A Spectroscopically Confirmed Excess Of 24 Μm Sources In A Super Galaxy Group At Z=0.37: Enhanced Dusty Star Formation Relative To The Cluster And Field Environment, Kim-Vy H. Tran, Amelie Saintonge, John Moustakas, Lei Bai, Anthony H. Gonzalez, Bradford P. Holden, Dennis Zaritsky, Stefan Kautsch

Chemistry and Physics Faculty Articles

To trace how dust-obscured star formation varies with environment, we compare the fraction of 24 μm sources in a super galaxy group to the field and a rich galaxy cluster at z ~ 0.35. We draw on multi-wavelength observations that combine Hubble, Chandra, and Spitzer imaging with extensive optical spectroscopy (>1800 redshifts) to isolate galaxies in each environment and thus ensure a uniform analysis. We focus on the four galaxy groups (σ_1D = 303-580 km s^–1) in supergroup 1120-12 that will merge to form a galaxy cluster comparable in mass to Coma. We find …

Forming Early-Type Galaxies In Groups Prior To Cluster Assembly, Stefan Kautsch, Anthony H. Gonzalez, Christian A. Soto, Kim-Vy H. Tran, Dennis Zaritsky, John Moustakas

Chemistry and Physics Faculty Articles

We study a unique protocluster of galaxies, the supergroup SG1120–1202. We quantify the degree to which morphological transformation of cluster galaxies occurs prior to cluster assembly in order to explain the observed early-type fractions in galaxy clusters at z = 0. SG1120–1202 at z ~ 0.37 is composed of four gravitationally bound groups that are expected to coalesce into a single cluster by z = 0. Using HST ACS observations, we compare the morphological fractions of the supergroup galaxies to those found in a range of environments. We find that the morphological fractions of early-type galaxies (~60%) and the ratio …

The Late Stellar Assembly Of Massive Cluster Galaxies Via Major Merging, Kim-Vy H. Tran, John Moustakas, Anthony H. Gonzalez, Lei Bai, Dennis Zaritsky, Stefan Kautsch

Chemistry and Physics Faculty Articles

We present multiwavelength observations of the brightest galaxies in four X-ray-luminous groups at z ~ 0.37 that will merge to form a cluster comparable in mass to Coma. Ordered by increasing stellar mass, the four brightest group galaxies (BGGs) present a time sequence where BGG-1, 2, and 3 are in merging systems and BGG-4 is a massive remnant (M_* = 6.7 × 10¹¹ M_☉). BGG-1 and 2 have bright, gravitationally bound companions and BGG-3 has two nuclei separated by only 2.5 kpc; thus, merging at z < 0.5 increases the BGG mass by ≳40% (t_MGR < 2 Gyr) and V-band luminosity by ~0.4 mag. The …

Structure Formation Inside Triaxial Dark Matter Halos: Galactic Disks, Bulges, And Bars, Clayton Heller, Isaac Shlosman, Evangelie Athanassoula

Physics & Astronomy: Faculty Publications

We investigate formation and evolution of galactic disks immersed in assembling live DM halos. Models have been evolved from cosmological initial conditions and represent the collapse of an isolated density perturbation. The baryons include gas participating in star formation (SF) and stars with the energy feedback onto the ISM. We find that (1) the triaxial halo figure tumbling is insignificant and the angular momentum (J) is channeled into the internal circulation, while the baryonic collapse is stopped by the centrifugal barrier; (2) density response of the (disk) baryons is out of phase with DM, thus washing out the …

Initial Mass Function Effects On The Colour Evolution Of Disk Galaxies, P. Westera, M. Samland, Stefan Kautsch, R. Buser, K. Ammon

Chemistry and Physics Faculty Articles

Aims. In this work, we want to find out if the IMF can be determined from colour images, integrated colours, or mass-to-light ratios, especially at high redshift, where galaxies cannot be resolved into individual stars, which would enable us to investigate dependencies of the IMF on cosmological epoch.

Methods. We use chemo-dynamical models to investigate the influence of the Initial Mass Function (IMF) on the evolution of a Milky Way-type disk galaxy, in particular of its colours.

Results. We find that the effect of the IMF on the internal gas absorption is larger than its effect on …

The Peculiar Motions Of Early-Type Galaxies In Two Distant Regions -- V. The Mg-- Relation, Age And Metallicity, M. Colless, D. Burstein, R. L. Davies, R. K. Mcmahan, R. P. Saglia, G. Wegner

Dartmouth Scholarship

We have examined the Mg—σ relation for early-type galaxies in the EFAR sample and its dependence on cluster properties. A comprehensive maximum likelihood treatment of the sample selection and measurement errors gives fits to the global Mg—σ relation of Mg b^′=0.131 log σ −0.131 and Mg₂=0.257 log σ −0.305. The slope of these relations is 25 per cent steeper than that obtained by most other authors owing to the reduced bias of our fitting method. The intrinsic scatter in the global Mg— σ relation is estimated to be 0.016 mag in Mg b^′ and 0.023 …