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Abstract
We observed two fields near M32 with the ACS/HRC on board the Hubble Space Telescope, located at distances of about 1.8' and 5.4' (hereafter F1 and F2, respectively) from the center of M32. To obtain a very detailed and deep color-magnitude diagram (CMD) and to look for short period variability, we obtained time-series imaging of each field in 32-orbit-long exposures using the F435W (B) and F555W (V) filters, spanning a temporal range of 2 days per filter. We focus on our detection of variability on RR Lyrae variable stars, which represents the only way to obtain information about the presence of a very old population (larger than 10 Gyr) in M32 from optical data. Here we present results obtained from the detection of 31 RR Lyrae in these fields: 17 in F1 and 14 in F2.
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Abstract
We determine the mass of the black hole at the center of the spiral galaxy NGC 4258 by constructing axisymmetric dynamical models of the galaxy. These models are constrained by high spatial resolution imaging and long-slit spectroscopy of the nuclear region obtained with the Hubble Space Telescope, complemented by ground-based observations extending to larger radii. Our best mass estimate is M-center dot = (3.3 +/- 0.2) x 10(7) M-circle dot for a distance of 7.28 Mpc (statistical errors only). This is within 15% of (3.82 +/- 0.01) x 10(7) M-circle dot, the mass determined from the kinematics of water masers (rescaled to the same distance), assuming they are in Keplerian rotation in a warped disk. The construction of accurate dynamical models of NGC 4258 is somewhat compromised by an unresolved active nucleus and color gradients; the latter caused by variations in the stellar population and/or obscuring dust. Depending on how these effects are treated, as well as on assumptions about the ellipticity and inclination of the galaxy, we obtain black hole masses ranging from 2.4 x 10(7) M-circle dot to 3.6 x 10(7) M-circle dot. This spread is mainly due to uncertainties in the stellar mass profile inside the central 2 '' (similar to 70 pc). Obscuration of high-velocity stars by circumnuclear dust (possibly associated with the masing disk) could lead to an underestimate of the black hole mass, which is hard to correct. These problems are not present in the similar to 30 other black hole mass determinations from stellar dynamics that have been published by us and other groups; thus, the relatively close agreement between the stellar-dynamical mass and the maser mass in NGC 4258 enhances our confidence in the black hole masses determined in other galaxies from stellar dynamics using similar methods and data of comparable quality.
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Abstract
Aims. We present the results from a comprehensive spectroscopic survey of the WINGS (WIde-field Nearby Galaxy-cluster Survey) clusters, a program called WINGS-SPE. The WINGS-SPE sample consists of 48 clusters, 22 of which are in the southern sky and 26 in the north. The main goals of this spectroscopic survey are: (1) to study the dynamics and kinematics of the WINGS clusters and their constituent galaxies, (2) to explore the link between the spectral properties and the morphological evolution in different density environments and across a wide range of cluster X-ray luminosities and optical properties.
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Abstract
Spitzer-MIPS 24 mu m observations and ground-based optical imaging and spectroscopy of the rich galaxy cluster Abell 851 at z = 0.41 are used to derive and compare star formation rates from the mid-IR 24 mu m and from [O II] lambda lambda 3727 emission. Many cluster galaxies have star formation rates SFR(24 mu m)/SFR([O II]) >> 1, indicative of star formation in regions highly obscured by dust. We focus on the substantial minority of A851 cluster members where strong Balmer absorption points to a starburst on a 10(8)-10(9) year timescale. As is typical, two types of galaxies with strong Balmer absorption are found in A851: with optical emission (starforming), and without optical emission (post-starburst). Our principal result is that the starforming variety, so-called e(a) galaxies, are mostly detected (9 out of 12) at 24 mu m-for these we find typically SFR(24 mu m)/SFR([O II]) similar to 4. Strong Balmer absorption and high values of SFR(24 mu m)/SFR([O II]) indicate moderately active starbursts (SB); both observations support the picture that e(a) galaxies are the active starbursts that feed the post-starburst population. While 24 mu m detections are frequent with Balmer-strong objects (even 6 out of 18 of the supposedly "post-starburst" galaxies are detected), only two out of seven of the continuously starforming 'e(c)' galaxies (with weak Balmer absorption) are detected-for them, SFR(24 mu m)/SFR([O II]) similar to 1. Their optical spectra resemble present-epoch spirals that dominate today's universe; we strengthen this association by showing that SFR(24 mu m)/SFR([O II]) similar to 1 is the norm today. That is, not just the amount of star formation but also its mode has evolved strongly from z similar to 0.4 to the present. We fit spectrophotometric models in order to measure the strength and duration of the bursts and to quantify the evolutionary sequence from active to post-starburst. Our results harden the evidence that moderately active starbursts are the defining feature of starforming cluster galaxies at z similar to 0.4.
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Abstract
Context. This is the second paper of a series devoted to the WIde Field Nearby Galaxy-cluster Survey (WINGS). WINGS is a long term project which is gathering wide-field, multi-band imaging and spectroscopy of galaxies in a complete sample of 77 X-ray selected, nearby clusters (0.04 < z < 0.07) located far from the galactic plane (vertical bar b vertical bar >= 20 degrees). The main goal of this project is to establish a local reference for evolutionary studies of galaxies and galaxy clusters.
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Abstract
We report five new measurements of central black hole masses based on Space Telescope Imaging Spectrograph and Wide Field Planetary Camera 2 observations with the Hubble Space Telescope (HST) and on axisymmetric, three-integral, Schwarzschild orbit-library kinematic models. We selected a sample of galaxies within a narrow range in velocity dispersion that cover a range of galaxy parameters (including Hubble type and core/power-law surface density profile) where we expected to be able to resolve the galaxy's sphere of influence based on the predicted value of the black hole mass from the M-sigma relation. We find masses for the following galaxies: NGC3585, M(BH) = 3.4(-0.6)(+1.5) x 10(8) M(circle dot;) NGC 3607, M(BH) = 1.2(-0.4)(+0.4) x 10(8) M(circle dot); NGC 4026, M(BH) = 2.1(-0.4)(+0.7) x 10(8) M(circle dot); and NGC 5576, M(BH) = 1.8(-0.4)(+0.3) x 10(8) M(circle dot), all significantly excluding M(BH) = 0. For NGC 3945, M(BH) = 9(-21)(+17) x 10(6) M(circle dot), which is significantly below predictions from M-sigma and M-L relations and consistent with MBH = 0, though the presence of a double bar in this galaxy may present problems for our axisymmetric code.
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Abstract
We report the discovery of a giant Ly alpha emitter (LAE) with a Spitzer/Infrared Array Camera (IRAC) counterpart near the reionization epoch at z = 6.595. The giant LAE is found from the extensive 1 deg(2) Subaru narrowband survey for z = 6.6 LAEs in the Subaru/XMM-Newton Deep Survey (SXDS) field, and subsequently identified by deep spectroscopy of Keck/DEIMOS and Magellan/IMACS. Among our 207 LAE candidates, this LAE is not only the brightest narrowband object with L(Ly alpha) = 3.9 +/- 0.2 x 10(43) erg s(-1) in our survey volume of 10(6) Mpc(3), but also a spatially extended Ly alpha nebula with the largest isophotal area whose major axis is at least similar or equal to 3 ''. This object is more likely to be a large Ly alpha nebula with a size of greater than or similar to 17 kpc than to be a strongly lensed galaxy by a foreground object. Our Keck spectrum with medium-high spectral and spatial resolutions suggests that the velocity width is nu(FWHM) = 251 +/- 21 km s(-1), and that the line-center velocity changes by similar or equal to 60 km s(-1) in a 10 kpc range. The stellar mass and star formation rate are estimated to be 0.9-5.0 x 10(10) M-circle dot and >34 M-circle dot yr(-1), respectively, from the combination of deep optical to infrared images of Subaru, UKIDSS-Ultra Deep Survey, and Spitzer/IRAC. Although the nature of this object is not yet clearly understood, this could be an important object for studying cooling clouds accreting onto a massive halo, or forming-massive galaxies with significant outflows contributing to cosmic reionization and metal enrichment of intergalactic medium.
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Abstract
We quantify the evolution of the spiral, S0 and elliptical fractions in galaxy clusters as a function of cluster velocity dispersion (sigma) and X-ray luminosity (L(X)) using a new database of 72 nearby clusters from the Wide-Field Nearby Galaxy-Cluster Survey (WINGS) combined with literature data at z = 0.5-1.2. Most WINGS clusters have sigma between 500 and 1100 km s(-1), and L(X) between 0.2 and 5 x 10(44) erg s(-1). The S0 fraction in clusters is known to increase with time at the expense of the spiral population. We find that the spiral and S0 fractions have evolved more strongly in lower sigma, less massive clusters, while we confirm that the proportion of ellipticals has remained unchanged. Our results demonstrate that morphological evolution since z = 1 is not confined to massive clusters, but is actually more pronounced in low-mass clusters, and therefore must originate either from secular (intrinsic) evolution and/or from environmental mechanisms that act preferentially in low-mass environments, or both in low-and high-mass systems. We also find that the evolution of the spiral fraction perfectly mirrors the evolution of the fraction of star-forming galaxies. Interestingly, at low-z the spiral fraction anticorrelates with L(X). Conversely, no correlation is observed with sigma. Given that both sigma and L(X) are tracers of the cluster mass, these results pose a challenge for current scenarios of morphological evolution in clusters.
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Abstract
We derive improved versions of the relations between supermassive black hole mass (MBH) and host-galaxy bulge velocity dispersion (sigma) and luminosity (L; the M-sigma and M-L relations), based on 49 M-BH measurements and 19 upper limits. Particular attention is paid to recovery of the intrinsic scatter (epsilon(0)) in both relations. We find log(M-BH/M-circle dot) = alpha + beta log(sigma/ 200 km s(-1)) with (alpha, beta, epsilon(0)) = (8.12 +/- 0.08, 4.24 +/- 0.41, 0.44 +/- 0.06) for all galaxies and (alpha, beta, epsilon(0)) = (8.23 +/- 0.08, 3.96 +/- 0.42, 0.31 +/- 0.06) for ellipticals. The results for ellipticals are consistent with previous studies, but the intrinsic scatter recovered for spirals is significantly larger. The scatter inferred reinforces the need for its consideration when calculating local black hole mass function based on the M-sigma relation, and further implies that there may be substantial selection bias in studies of the evolution of the M-sigma relation. We estimate the M-L relationship as log(M-BH/M-circle dot) = alpha + beta log(L-V/10(11) L-circle dot,L- V) of (alpha, beta, epsilon(0)) = (8.95 +/- 0.11, 1.11 +/- 0.18, 0.38 +/- 0.09); using only early-type galaxies. These results appear to be insensitive to a wide range of assumptions about the measurement errors and the distribution of intrinsic scatter. We show that culling the sample according to the resolution of the black hole's sphere of influence biases the relations to larger mean masses, larger slopes, and incorrect intrinsic residuals.
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