arXiv subjects

Riccardo Giovanelli

Publications and source records attributed to Riccardo Giovanelli.

At least 127 records · Page 7Linked to original sources

arXiv2004

M/L, H-alpha Rotation Curves, and HI Measurements for 329 Nearby Cluster and Field Spirals: I. Data

A survey of 329 nearby galaxies (redshift z < 0.045) has been conducted to study the distribution of mass and light within spiral galaxies over a range of environments. The 18 observed clusters and groups span a range of richness, density, and X-ray temperature, and are supplemented by a set of 30 isolated field galaxies. Optical spectroscopy taken with the 200-inch Hale Telescope provides separately resolved H-alpha and [NII] major axis rotation curves for the complete set of galaxies, which are analyzed to yield velocity widths and profile shapes, extents and gradients. HI line profiles provide an independent velocity width measurement and a measure of HI gas mass and distribution. I-band images are used to deconvolve profiles into disk and bulge components, to determine global luminosities and ellipticities, and to check morphological classification. These data are combined to form a unified data set ideal for the study of the effects of environment upon galaxy evolution.

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arXiv2004

M/L, H-alpha Rotation Curves, and HI Measurements for 329 Nearby Cluster and Field Spirals: II. Evidence for Galaxy Infall

We have conducted a study of optical and HI properties of spiral galaxies (size, luminosity, H-alpha flux distribution, circular velocity, HI gas mass) to explore the role of gas stripping as a driver of morphological evolution in clusters. We find a strong correlation between the spiral and S0 fractions within clusters, and the spiral fraction scales tightly with cluster X-ray gas luminosity. We explore young star formation and identify spirals that are (1) asymmetric, with truncated H-alpha emission and HI gas reservoirs on the leading edge of the disk, on a first pass through the dense intracluster medium in the cores of rich clusters; (2) strongly HI deficient and stripped, with star formation confined to the inner 5 kpc/h and 3 disk scale lengths; (3) reddened, extremely HI deficient and quenched, where star formation has been halted across the entire disk. We propose that these spirals are in successive stages of morphological transformation, between infalling field spirals and cluster S0s, and that the process which acts to remove the HI gas reservoir suppresses new star formation on a similarly fast timescale. These data suggest that gas stripping plays a significant role in morphological transformation and rapid truncation of star formation across the disk.

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arXiv2004

M/L, H-alpha Rotation Curves, and HI Measurements for 329 Nearby Cluster and Field Spirals: III. Evolutionin Fundamental Galaxy Parameters

We have conducted a study of optical and HI properties of spiral galaxies (size, luminosity, H-alpha flux distribution, circular velocity, HI gas mass) to investigate causes (e.g., nature versus nurture) for variation within the cluster environment. We find HI deficient cluster galaxies to be offset in Fundamental Plane space, with disk scale lengths decreased by a factor of 25%. This may be a relic of early galaxy formation, caused by the disk coalescing out of a smaller, denser halo (e.g., higher concentration index) or by truncation of the hot gas envelope due to the enhanced local density of neighbors, though we cannot completely rule out the effect of the gas stripping process. The spatial extent of H-alpha flux and the B-band radius also decreases, but only in early type spirals, suggesting that gas removal is less efficient within steeper potential wells (or that stripped late type spirals are quickly rendered unrecognizable). We find no significant trend in stellar mass-to-light ratios or circular velocities with HI gas content, morphological type, or clustercentric radius, for star forming spiral galaxies throughout the clusters. These data support the findings of a companion paper that gas stripping promotes a rapid truncation of star formation across the disk, and could be interpreted as weak support for dark matter domination over baryons in the inner regions of spiral galaxies.

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arXiv2003

An estimate of Ω_m without priors

Using mean relative peculiar velocity measurements for pairs of galaxies, we estimate the cosmological density parameter $Ω_m$ and the amplitude of density fluctuations $σ_8$. Our results suggest that our statistic is a robust and reproducible measure of the mean pairwise velocity and thereby the $Ω_m$ parameter. We get $Ω_m = 0.30^{+0.17}_{-0.07}$ and $σ_8 = 1.13^{+0.22}_{-0.23}$. These estimates do not depend on prior assumptions on the adiabaticity of the initial density fluctuations, the ionization history, or the values of other cosmological parameters.

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arXiv2003

Internal Extinction in Spiral Galaxies in the Near Infrared

In order to study the effects of internal extinction in spiral galaxies we search for correlations of near infrared (NIR) photometric parameters with inclination. We use data from the 2 Micron All-Sky Survey (2MASS) Extended Source Catalog (XSC) on 15,224 spiral galaxies for which we also have redshifts. For 3035 of the galaxies, I-band photometry is available which is included in the analysis. From the simple dependence of reddening on inclination we derive a lower limit to the difference in magnitude between the face-on and edge-on aspect of 0.9, 0.3 and 0.1 magnitudes in I (0.81 um), J (1.25 um) and H (1.65 um) bands. We find that the faintest isophotal radius reported in the XSC (at the 21st mag/arc sq level) is closer to the centers of the galaxies than other common isophotal measures (e.g. the 23.5 mag/arc sq radius in I-band), and argue that it should not be assumed to represent an outer isophote at which galaxies are transparent at all viewing angles. A simple linear extinction law (i.e. Delta M = gamma log(a/b)) is not adequate for the full range of disk inclinations and we adopt both a bi-linear and a quadratic law. A simple photometric model is used to explain the observed behavior. Internal extinction depends on galaxy luminosity. We show that for galaxies with a K total magnitude dimmer than -20, -20.7 and -20.9 the data indicates zero extinction in J, H and K respectively, while disk opacity increases monotonically with increasing disk luminosity.

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arXiv2003

A Search for 6.7 GHz Methanol Masers in OH Megamaser Galaxies at 0.11<z<0.27

We report the results of a search for 6.7 GHz methanol (CH3OH) maser emission in OH megamaser galaxies at 0.11<z<0.27. No detections were made in the 25 objects observed down to rms noise levels of roughly 0.6 mJy in 150 kHz channels. The OH megamaser sample includes OH emission of all observed types: narrow and broad, physically compact and extended, variable and quiescent, and from simple single lines to multi-component complexes to lines with high velocity wings. Our null result indicates, for the widest possible range of OH megamaser environments, that methanol masing does not scale with OH from Galactic masers to megamasers. These observations, however, are not sensitive enough to rule out methanol masing that scales with star formation from Galactic compact HII regions to starbursts associated with major mergers. This and previous work suggest that OH megamasers do not represent large ensembles of individual masers associated with star forming regions. Maser models combined with observational constraints on the physical settings of OH megamasers indicate that 6.7 GHz methanol megamasers will not be detected by this survey if T(dust) < 100 K or if n(CH3OH) < n(OH).

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arXiv2002

A Search for OH Megamasers at z > 0.1. III. The Complete Survey

We present the final results from the Arecibo Observatory OH megamaser survey. We discuss in detail the properties of the remaining 18 OH megamasers detected in the survey, including 3 redetections. We place upper limits on the OH emission from 85 nondetections and examine the properties of 25 ambiguous cases for which the presence or absence of OH emission could not be determined. The complete survey has discovered 50 new OH megamasers (OHMs) in (ultra)luminous infrared galaxies ([U]LIRGs) which doubles the sample of known OHMs and increases the sample at z>0.1 sevenfold. The Arecibo OH megamaser survey indicates that the OHM fraction in LIRGs is an increasing function of the far-IR luminosity (L_{FIR}) and far-IR color, reaching a fraction of roughly one third in the warmest ULIRGs. Significant relationships between OHMs and their hosts are few, primarily due to a mismatch in size scales of measured properties and an intrinsic scatter in OHM properties roughly equal to the span of the dataset. We investigate relationships between OHMs and their hosts with a variety of statistical tools including survival analysis, partial correlation coefficients, and a principal component analysis. There is no apparent OH megamaser ``fundamental plane.'' We compile data on all previously known OHMs and evaluate the possible mechanisms and relationships responsible for OHM production in merging systems. The OH-FIR relationship is reexamined using the doubled OHM sample and found to be significantly flatter than previously thought: L_{OH} ~ L_{FIR}^{1.2 +/- 0.1}. This near-linear dependence suggests a mixture of saturated and unsaturated masers, either within individual galaxies or across the sample.

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arXiv2002

The Inner Scale Length of Spiral Galaxy Rotation Curves

We use the tapering effect of Halpha/[NII] rotation curves of spiral galaxies first noted by Goad & Roberts (1981) to investigate the internal extinction in disks. The scale length of exponential fits to the inner part of rotation curves depends strongly on the disk axial ratio. Preliminary modelling of the effect implies substantial opacity of the central parts of disks at a wavelength of 0.66 μ. In addition, the average kinematic scale length of rotation curves, when corrected to face--on perspective, has a nearly constant value of about 1.7 h^{-1} kpc, for all luminosity classes. The interpretation of that effect, as the result of the increasing dominance of the baryonic mass in the inner parts of galaxies, yields a mean baryonic mass--to--light ratio in the I band Υ_I= 2.7h M_sun/L_{sun,I}, within the inner 1.7 h^{-1} kpc of disks.

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arXiv2002

The OH Megamaser Luminosity Function

We present the 1667 MHz OH megamaser luminosity function derived from a single flux-limited survey. The Arecibo Observatory OH megamaser (OHM) survey has doubled the number of known OH megamasers, and we list the complete catalog of OHMs detected by the survey here, including three redetections of known OHMs. OHMs are produced in major galaxy mergers which are (ultra)luminous in the far-infrared. The OH luminosity function follows a power law in integrated line luminosity, $Φ\propto L_{OH}^{-0.64}$ per Mpc^3 per dex, and is well-sampled for 10^{2.2} L(sun) < L_{OH} < 10^{3.8} L(sun). The OH luminosity function is incorporated into predictions of the detectability and areal density of OHMs in high redshift OH surveys for a variety of current and planned telescopes and merging evolution scenarios parameterized by (1+z)^m in the merger rate ranging from m=0 (no evolution) to m=8 (extreme evolution). Up to dozens of OHMs may be detected per square degree per 50 MHz by a survey reaching an rms noise of 100 microJy per 0.1 MHz channel. An adequately sensitive ``OH Deep Field'' would significantly constrain the evolution exponent m even if no detections are made. In addition to serving as luminous tracers of massive mergers, OHMs may also trace highly obscured nuclear starburst activity and the formation of binary supermassive black holes.

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arXiv2002

The Discovery of Time Variability in OH Megamasers

We report the discovery of variability in the OH megamaser in IRAS 21272+2514 at z=0.15. This is the first OH megamaser (OHM) observed to vary in time. The variation is broadband, spanning 0.5-1.5 MHz or 100-300 km/s in the rest frame, and strong, showing rms modulations of 10%-15% while the largest change in flux density between extremal epochs is 34%. Timescales sampled range from 39 to 821 days, and the characteristic modulation timescale is likely to be less than the shortest time baseline. The source of modulation is currently ambiguous, although we favor interstellar scintillation. Best estimates of the size scales of the 1667 MHz OH line features obtained from refractive interstellar scintillation models constrain variable features to be smaller than 2 pc, and quiescent features to be larger than a few pc. Compact masers account for roughly 27%-58% of the total OH emission in this source. Accelerations in spectral lines are generally constrained to be less than 3 km/s/yr, but acceleration of this magnitude is suggested in one of the quiescent spectral components and merits further study.

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arXiv2001

The Optical/Infrared Astronomical Quality of High Atacama Sites. I. Preliminary Results of Optical Seeing

The region surrounding the Llano de Chajnantor, a high altitude plateau in the Atacama Desert in northern Chile, has caught the attention of the astronomical community for its potential as an observatory site. Combining high elevation and extremely low atmospheric water content, the Llano has been chosen as the future site of the Atacama Large Millimeter Array. We have initiated a campaign to investigate the astronomical potential of the region in the optical/infrared. Here, we report on an aspect of our campaign aimed at establishing a seeing benchmark to be used as a reference for future activities in the region. After a brief description of the region and its climate, we describe the results of an astronomical seeing campaign, carried out with a Differential Image Motion Monitor that operates at 0.5 micron wavelength. The seeing at the Llano level of 5000 m, measured over 7 nights in May 1998, yielded a median FWHM of 1.1". However, the seeing decreased to 0.7" at a modest 100 m gain above the plateau (Cerro Chico), as measured over 38 nights spread between July 1998 and October 2000. Neither of these represents the best seeing expected in the region; the set of measurements provides a reference base for simultaneous dual runs at Cerro Chico and at other sites of interest in the region, currently underway. A comparison between simultaneous measurements at Cerro Chico and Cerro Paranal indicates that seeing at Cerro Chico is about 12% better than at Paranal. The percentage of optically photometric nights in the Chajnantor region is about 60%, while that of nights useful for astronomical work is near 80%.

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arXiv2001

The Optical/Infrared Astronomical Quality of High Atacama Sites. II. Infrared Characteristics

We discuss properties of the atmospheric water vapor above the high Andean plateau region known as the Llano de Chajnantor, in the Atacama Desert of northern Chile. A combination of radiometric and radiosonde measurements indicate that the median column of precipitable water vapor (PWV) above the plateau at an elevation of 5000 m is approximately 1.2 mm. The exponential scaleheight of the water vapor density in the median Chajnantor atmosphere is 1.13 km; the median PWV is 0.5 mm above an elevation of 5750 m. Both of these numbers appear to be lower at night. Annual, diurnal and other dependences of PWV and its scaleheight are discussed, as well as the occurrence of temperature inversion layers below the elevation of peaks surrounding the plateau. We estimate the background for infrared observations and sensitivities for broad band and high resolution spectroscopy. The results suggest that exceptional atmospheric conditions are present in the region, yielding high infrared transparency and high sensitivity for future ground-based infrared telescopes.

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arXiv2001

A Search for OH Megamasers at z > 0.1. II. Further Results

We present current results of an ongoing survey for OH megamasers in luminous infrared galaxies at the Arecibo Observatory. The survey is now two-thirds complete, and has resulted in the discovery of 35 new OH megamasers at z > 0.1, 24 of which are presented in this paper. We discuss the properties of each source in detail, including an exhaustive survey of the literature. We also place upper limits on the OH emission from 107 nondetections and list their IR, radio, and optical properties. The survey detection rate is 1 OH megamaser for every 6 candidates overall, but is a strong function of the far IR luminosity of candidates and may depend on merger stage or on the central engine responsible for the IR luminosity in the merging galaxy pair. We also report the detection of IRAS 12032+1707, a new OH gigamaser.

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arXiv2000

Optical Seeing and Infrared Atmospheric Transparency in the Upper Atacama Desert

With plans to build a large IR/optical telescope in the Atacama Desert, a site survey campaign has been underway since 1998 to characterize the optical seeing and the IR transparency in the Chajnantor Plateau region. Preliminary results indicate that the Chajnantor region offers excellent astronomical observing conditions in the optical and IR. The region is isolated yet easy to reach, and high quality services are available nearby. We can expect to find: median optical FWHM seeing approaching values of 0.5"--0.6", a percentage of photometric nights of 65% or better, of astronomically useful nights in excess of 80% and median PWV well below 1 mm (with best quartile below 0.5 mm).

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arXiv2000

Signatures of Galaxy-Cluster Interactions: Spiral Galaxy Rotation Curve Asymmetry, Shape, and Extent

The environmental dependencies of the characteristics of spiral galaxy rotation curves are studied in this work. We use our large, homogeneously collected sample of 510 cluster spiral galaxy rotation curves to test the claim that the shape of a galaxy's rotation curve strongly depends on its location within the cluster, and thus presumably on the strength of the local intracluster medium and on the frequency and strength of tidal interactions with the cluster and cluster galaxies. Our data do not corroborate such a scenario, consistent with the fact that Tully-Fisher residuals are independent of galaxy location within the cluster; while the average late-type spiral galaxy shows more rise in the outer parts of its rotation curve than does the typical early-type spiral galaxy, there is no apparent trend for either subset with cluster environment. We also investigate as a function of cluster environment rotation curve asymmetry and the radial distribution of H II region tracers within galactic disks. Mild trends with projected cluster-centric distance are observed: (i) the (normalized) radial extent of optical line emission averaged over all spiral galaxy types shows a 4%+/-2% increase per Mpc of galaxy-cluster core separation, and (ii) rotation curve asymmetry falls by a factor of two between the inner and outer cluster for early-type spirals (a negligible decrease is found for late-type spirals). Such trends are consistent with spiral disk perturbations or even the stripping of the diffuse, outermost gaseous regions within the disks as galaxies pass through the dense cluster cores.

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arXiv2000

The Arecibo OH Megamaser Survey and the Galaxy Merger Rate

We present the current results of a survey for OH megamasers (OHMs) underway at the Arecibo Observatory. The survey is 2/3 complete and has produced a high OHM detection rate (1 in 6) from a redshift-selected sample of IRAS galaxies. The survey will relate the OHM luminosity function to the galaxy merger rate, allowing subsequent blind OHM surveys to measure the galaxy merger rate as a function of cosmic time. The survey has also made the first detection of strong variability in OHMs. Variability will provide a powerful tool for understanding the small-scale physical settings and mechanisms of OHMs.

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arXiv2000

The HI Content of Spirals. II. Gas Deficiency in Cluster Galaxies

We derive the atomic hydrogen content for a total of 1900 spirals in the fields of eighteen nearby clusters. By comparing the HI deficiency distributions of the galaxies inside of and outside of one Abell radius of each cluster, we find that two thirds of the clusters in our sample show a dearth of neutral gas in their interiors. Possible connections between the gaseous deficiency and the characteristics of both the underlying galaxies and their environment are investigated in order to gain insight into the mechanisms responsible for HI depletion. While we do not find a statistically significant variation of the fraction of HI-deficient spirals in a cluster with its global properties, a number of correlations emerge that argue in favor of the interplay between spiral disks and their environment. In the clusters in which neutral gas deficiency is pronounced, we see clear indications that the degree of HI depletion is related to the morphology of the galaxies and not to their optical size: early-type and, probably, dwarf spirals are more easily emptied of gas than the intermediate Sbc--Sc types. The wealth of 21-cm data collected for the Virgo region has made it possible to study the 2D pattern of HI deficiency in that cluster. We also find evidence that gas-poor spirals in HI-deficient clusters move on orbits more radial than those of the gas-rich objects. The implications of all these results on models of how galaxies interact with their environment are reviewed. Hydrodynamic effects appear as the most plausible cause of HI removal. (abridged)

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arXiv2000

Gravitational Lensing by Nearby Clusters of Galaxies

We present an estimation of the expected number of arcs and arclets in a sample of nearby (z<0.1) clusters of galaxies, that takes into account the magnitude limit of the objects as well as seeing effects. We show that strong lensing effects are not common, but also they are not as rare as usually stated. Indeed, for a given cluster, they present a strong dependence with the magnitude limit adopted in the analysis and the seeing of the observations. We also describe the procedures and results of a search for lensing effects in a sample of 33 clusters spanning the redshift range of 0.014 to 0.076, representative of the local cluster distribution. This search produced two arc candidates. The first one is in A3408 (z=0.042), the same arc previously discovered by Campusano & Hardy (1996), with z=0.073 and associated to the brightest cluster galaxy. The second candidate is in the cluster A3266 (z=0.059) and is near a bright elliptical outside the cluster center, requiring the presence of a very massive sub-structure around this galaxy to be produced by gravitational lensing.

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