Eleazar R. Carrasco

Gemini K-band NIRI Adaptive Optics Observations of massive galaxies at 1 < z < 2

We present deep K-band adaptive-optics observations of eight very massive (M� � 4 × 10 11 M� ) galaxies at 1 < z < 2 utilizing the Gemini NIRI/Altair Laser Guide System. These systems are selected from the Palomar Observatory Wide-Field Infrared (POWIR) survey, and are amongst the most massive field galaxies at these epochs. The depth and high spatial resolution of our images allow us to explore for the first time the stellar mass surface density distribution of massive distant galaxies from 1 to 15 kpc on an individual galaxy basis, rather than on stacked images. We confirm that some of these massive objects are extremely compact with measured effective radii between 0: 00 1 - 0: 00 2, giving sizes which are . 2 kpc, a factor of �7 smaller in effective radii than similar mass galaxies today. Examining stellar mass surface densities as a function of fixed physical aperture, we find an over-density of material within the inner profiles, and an under-density in the outer profile, within these high-z galaxies compared with similar mass galaxies in the local universe. Consequently, massive galaxies should evolve in a way to decrease the stellar mass density in their inner region, and at the same time creating more extensive outer light envelopes. We furthermore show that �38%±20% of our sample contains evidence for a disturbed outer stellar matter distribution suggesting that these galaxies are undergoing a recent dynamical episode, such as a merger or accretion event. We calculate that massive galaxies at z < 2 will undergo on the order of five of these events, a much higher rate than observed for major mergers, suggesting that these galaxies are growing in size and stellar mass in part through minor mergers during this epoch.

Early-type Galaxies at z = 1.3. I. The Lynx Supercluster: Cluster and Groups at z = 1.3. Morphology and Color-Magnitude Relation

We confirm the detection of three groups in the Lynx supercluster, at z ≈ 1.3, through spectroscopic follow-up and X-ray imaging, and we give estimates for their redshifts and masses. We study the properties of the group galaxies compared to the two central clusters, RX J0849+4452 and RX J0848+4453. Using spectroscopic follow-up and multi-wavelength photometric redshifts, we select 89 galaxies in the clusters, of which 41 are spectroscopically confirmed, and 74 galaxies in the groups, of which 25 are spectroscopically confirmed. We morphologically classify galaxies by visual inspection, noting that our early-type galaxy (ETG) sample would have been contaminated at the 30%-40% level by simple automated classification methods (e.g., based on Sersic index). In luminosity-selected samples, both clusters and groups show high fractions of bulge-dominated galaxies with a diffuse component that we visually identified as a disk and which we classified as bulge-dominated spirals, e.g., Sas. The ETG fractions never rise above ≈50% in the clusters, which is low compared to the fractions observed in other massive clusters at z ≈ 1. In the groups, ETG fractions never exceed ≈25%. However, overall bulge-dominated galaxy fractions (ETG plus Sas) are similar to those observed for ETGs in clusters at z ~ 1. Bulge-dominated galaxies visually classified as spirals might also be ETGs with tidal features or merger remnants. They are mainly red and passive, and span a large range in luminosity. Their star formation seems to have been quenched before experiencing a morphological transformation. Because their fraction is smaller at lower redshifts, they might be the spiral population that evolves into ETGs. For mass-selected samples of galaxies with masses M > 10^(10.6) M_☉ within Σ > 500 Mpc^(–2), the ETG and overall bulge-dominated galaxy fractions show no significant evolution with respect to local clusters, suggesting that morphological transformations might occur at lower masses and densities. The ETG mass-size relation shows evolution toward smaller sizes at higher redshift in both clusters and groups, while the late-type mass-size relation matches that observed locally. When compared to the clusters, the group ETG red sequence shows lower zero points (at ~2σ) and larger scatters, both expected to be an indication of a younger galaxy population. However, we show that any allowed difference between the age in groups and clusters would be small when compared to the differences in age in galaxies of different masses.

A likely decade-long sustained tidal disruption event

Multiwavelength flares from tidal disruption and accretion of stars can be used to find and study otherwise dormant massive black holes in galactic nuclei1. Previous well-monitored candidate flares were short-lived, with most emission confined to within ∼1 year2–5. Here we report the discovery of a well-observed super-long (>11 years) luminous X-ray flare from the nuclear region of a dwarf starburst galaxy. After an apparently fast rise within ∼4 months a decade ago, the X-ray luminosity, though showing a weak trend of decay, has been persistently high at around the Eddington limit (when the radiation pressure balances the gravitational force). The X-ray spectra are soft — steeply declining towards higher energies — and can be described with Comptonized emission from an optically thick low-temperature corona, a super-Eddington accretion signature often observed in accreting stellar-mass black holes6. Dramatic spectral softening was also caught in one recent observation, implying either a temporary transition from the super-Eddington accretion state to the standard thermal state, or the presence of a transient highly blueshifted (∼0.36c) warm absorber. All these properties in concert suggest a tidal disruption event with an unusually long super-Eddington accretion phase that has never before been observed. An uncharacteristically long stellar disruption from a supermassive black hole has been unravelling over the last decade. Spectral information implies very efficient accretion but recent observations hint at a transition to a less extreme accretion mode.

DISCOVERY OF THE CANDIDATE OFF-NUCLEAR ULTRASOFT HYPER-LUMINOUS X-RAY SOURCE 3XMM J141711.1+522541

We report the discovery of an off-nuclear ultrasoft hyper-luminous X-ray source candidate 3XMM J141711.1+522541 in the inactive S0 galaxy SDSS J141711.07+522540.8 (z=0.41827, d_L=2.3 Gpc) in the Extended Groth Strip. It is located at a projected offset of ~1.0 (5.2 kpc) from the nucleus of the galaxy and was serendipitously detected in five XMM-Newton observations in 2000 July. Two observations have enough counts and can be fitted with a standard thermal disk with an apparent inner disk temperature kT_MCD ~ 0.13 keV and a 0.28-14.2 keV unabsorbed luminosity L_X ~ 4X10^{43} erg/s in the source rest frame. The source was still detected in three Chandra observations in 2002 August, with similarily ultrasoft but fainter spectra (kT_MCD ~ 0.17 keV, L_X ~ 0.5X10^{43} erg/s). It was not detected in later observations, including two by Chandra in 2005 October, one by XMM-Newton in 2014 January, and two by Chandra in 2014 September-October, implying a long-term flux variation factor of >14. Therefore the source could be a transient with an outburst in 2000-2002. It has a faint optical counterpart candidate, with apparent magnitudes of m_F606W=26.3 AB mag and m_F814W=25.5 AB mag in 2004 December (implying an absolute V-band magnitude of ~-15.9 AB mag). We discuss various explanations for the source and find that it is best explained as a massive black hole (BH) embedded in the nucleus of a possibly stripped satellite galaxy, with the X-ray outburst due to tidal disruption of a surrounding star by the BH. The BH mass is ~10^5 Msun, assuming the peak X-ray luminosity at around the Eddington limit.

Low X-ray luminosity galaxy clusters – II. Optical properties and morphological content at 0.18 < z < 0.70

Fil: Nilo Castellon, Jose Luis Emilio. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Astronomia Teorica y Experimental. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba. Instituto de Astronomia Teorica y Experimental; Argentina

First performance of the GeMS + GMOS system – 1. Imaging

During the commissioning of the Gemini MCAO System (GeMS), we had the opportunity to obtain data with the Gemini Multi-Object Spectrograph (GMOS), the most utilised instrument at Gemini South Observatory, in March and May 2012. Several globular clusters were observed in imaging mode that allowed us to study the performance of this new and untested combination. GMOS is a visible instrument, hence pushing MCAO toward the visible.We report here on the results with the GMOS instruments, derive photometric performance in term of Full Width Half Maximum (FWHM) and throughput. In most of the cases, we obtained an improvement factor of at least 2 against the natural seeing. This result also depends on the Natural Guide Star constellation selected for the observations and we then study the impact of the guide star selection on the FWHM performance.We also derive a first astrometric analysis showing that the GeMS+GMOS system provide an absolute astrometric precision better than 8mas and a relative astrometric precision lower than 50 mas.

The stellar mass–size relation for cluster galaxies at z = 1 with high angular resolution from the Gemini/GeMS multiconjugate adaptive optics system

We present the stellar mass - size relation for 49 galaxies within the

GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle

z

The Cheshire Cat Gravitational Lens: The Formation of a Massive Fossil Group

= 1.067 cluster SPT-CL J0546

A luminous X-ray outburst from an intermediate-mass black hole in an off-centre star cluster

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