arXiv subjects

D. Calzetti

Publications and source records attributed to D. Calzetti.

178 records · Page 10Linked to original sources

arXiv2001

NICMOS Observations of Extragalactic Cepheids. I. Photometry Database and a Test of the Standard Extinction Law

We present the results of near-infrared observations of extragalactic Cepheids made with the Near Infrared Camera and Multi-Object Spectrometer on board the Hubble Space Telescope. The variables are located in the galaxies IC 1613, IC 4182, M 31, M 81, M 101, NGC 925, NGC 1365, NGC 2090, NGC 3198, NGC 3621, NGC 4496A and NGC 4536. All fields were observed in the F160W bandpass; additional images were obtained in the F110W and F205W filters. Photometry was performed using the DAOPHOT II/ALLSTAR package. Self-consistent distance moduli and color excesses were obtained by fitting Period-Luminosity relations in the H, I and V bands. Our results support the assumption of a standard reddening law adopted by the HST Key Project on the Extragalactic Distance Scale. A companion paper will determine true distance moduli and explore the effects of metallicity on the Cepheid distance scale.

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arXiv2000

The Properties of High Redshift Galaxies

In recent years, a variety of techniques at optical, near-infrared, sub-mm, and radio wavelengths have opened complementary windows on the high-redshift Universe. Here we review the current understanding of the general properties of the z>~2 galaxies detected in the optical (Lyman-break galaxies) and in the sub-mm (SCUBA sources). We list some of the key questions that need to be answered in order to understand the nature and evolution of the high-redshift galaxies. Wherever possible, we present tentative answers given so far to those questions, in particular on the low-redshift couterparts of the high-redshift galaxies, on the impact of dust obscuration on the observed quantities, and on physical characteristics of the high-z systems as inferred from observations.

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arXiv2000

NICMOS Imaging of the Host Galaxies of z ~ 2 - 3 Radio-Quiet Quasars

We have made a deep NICMOS imaging study of a sample of 5 z ~ 2 - 3 radio-quiet quasars with low absolute nuclear luminosities, and we have detected apparent host galaxies in all of these. Most of the hosts have luminosities approximately equal to present-day L*, with a range from 0.2 L* to about 4 L*. These host galaxies have magnitudes and sizes consistent with those of the Lyman break galaxies at similar redshifts and at similar rest wavelengths, but are about two magnitudes fainter than high-z powerful radio galaxies. The hosts of our high-z sample are comparable to or less luminous than the hosts of the low-z RQQs with similar nuclear absolute magnitudes. However, the high z galaxies are more compact than the hosts of the low z quasars, and probably have only 10 - 20% of the stellar mass of their low-z counterparts. Application of the M(bulge)/M(BH) relation found for present-day spheroids to the stellar masses implied for the high z host galaxies would indicate that they contain black holes with masses around 10^8 Msolar. Comparison to their nuclear magnitudes implies accretion rates that are near or at the Eddington limit. Although these high z hosts already contain supermassive black holes, the galaxies will need to grow significantly to evolve into present-day L* galaxies. These results are basically consistent with theoretical predictions for the hierarchical buildup of the galaxy host and its relation to the central supermassive black hole.

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arXiv2000

Hiden Star Formation: The Ultraviolet Perspective

Many recent estimates of the star formation rate density at high redshift rely on rest-frame ultraviolet (UV) data. These are highly sensitive to dust absorption. Applying a correlation between the far-infrared (FIR) to UV flux ratio and UV color found in a local starbursts to galaxy samples out to z ~ 3, one can account for most of the FIR background. However, the correlation is based on a sample that does not include the most extreme starbursts, Ultra Luminous Infrared Galaxies (ULIGs). Our new UV images of ULIGs show that their FIR fluxes are underpredicted by this correlation by factors ranging from 7 to 70. We discuss how ULIGs compare to the various types of high-z galaxies: sub-mm sources, Lyman Break Galaxies, and Extremely Red Objects.

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arXiv1999

The Evolution of the Interstellar Medium Around Young Stellar Clusters

The interplay between the ISM and the massive stars formed in clusters and, more generally, in recent events of star formation is reviewed via the global effects each has on the other. The pre-existing environment affects the properties of the massive stars, the duration of the star-forming event and could potentially affect the IMF. The collective effect of massive-star winds and supernova explosions creates a structured ISM by forming bubbles, supershells and, in more extreme cases, by inducing large-scale gas outflows. Gas/dust removal may quench star formation in young stellar clusters. Conversely, supernova-driven shocks may trigger star formation in molecular clouds surrounding the stellar clusters. Metal ejection from the massive stars is responsible for the pollution of the ISM and, if the metal-rich gas can escape the galaxy's gravitational potential, of the IGM. The environment where stellar clusters form is populated by a diffuse stellar population which contributes between 50% and 80% of the total UV light. The investigation of the nature of the diffuse UV light is the subject of a study employing HST STIS spectroscopy, whose preliminary results are presented and briefly discussed.

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arXiv1999

The Dust Content and Opacity of Actively Star-Forming Galaxies

(Abridged) We present far-infrared (FIR) photometry at 150 micron and 205 micron of eight low-redshift starburst galaxies obtained with the ISO Photometer. Five of the eight galaxies are detected in both wavebands and these data are used, in conjunction with IRAS archival photometry, to model the dust emission at lambda>40 micron. The FIR spectral energy distributions (SEDs) are best fitted by a combination of two modified Planck functions, with T~40-55 K (warm dust) and T~20-23 K (cool dust), and with a dust emissivity index epsilon=2. The cool dust can be a major contributor to the FIR emission of starburst galaxies, representing up to 60% of the total flux. This component is heated not only by the general interstellar radiation field, but also by the starburst itself. The cool dust mass is up to ~150 times larger than the warm dust mass, bringing the gas-to-dust ratios of the starbursts in our sample close to Milky Way values, once rescaled for the appropriate metallicity. The ratio between the total dust FIR emission in the range 1-1000 micron and the IRAS FIR emission in the range 40-120 micron is ~1.75, with small variations from galaxy to galaxy. The FIR emission predicted by the dust reddening of the UV-to-nearIR stellar emission is within a factor ~2 of the observed value in individual galaxies and within 20% when averaged over a large sample. If our sample of local starbursts is representative of high-redshift (z>1), UV-bright, star-forming galaxies, these galaxies' FIR emission will be generally undetected in sub-mm surveys, unless (1) their bolometric luminosity is comparable to or larger than that of ultraluminous FIR galaxies and (2) their FIR SED contains a cool dust component.

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arXiv1999

HST NICMOS Imaging of z ~ 2 to 3 radio-quiet quasars

We will present the results of a NICMOS H-band imaging survey of a small sample of z ~ 2 to 3 radio-quiet quasars. We have resolved extension in at least 4 of 5 objects and find evidence for a wide range in the morphologies and magnitudes of these hosts. The host galaxy luminosities range from sub-L* to about 4 L*, with most of the hosts having luminosities about L*. These host galaxies have magnitudes and sizes consistent with those of the Ly break galaxies at similar redshifts and at similar rest wavelengths, but are about a magnitude fainter than the comparable 6C radio galaxies. One residual host component is not centered on the quasar nucleus, and several have close companions (within ~10 kpc), indications that these systems are possibly in some phase of a merger process.

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arXiv1999

Panchromatic Study of Nearby UV-Bright Starburst Galaxies: Implications for Massive Star Formation and High Redshift Galaxies

We present a panchromatic study of nearby starburst galaxies from the ultraviolet to the visible, including narrow band H(alpha) using WIYN and HST data, to determine how star formation processes affect the morphology and integrated fluxes of nearby starbursts. We find the UV/H(alpha) morphology of starbursts tend to differ, although not in a standard or predictable manner. From our sample of six nearby starbursts, three systems show a good correlation between UV and H(alpha) fluxes, but we find differences in UV and H(alpha) morphology between the other three. Occasionally we find systems with well defined H II regions without the corresponding brightness in the UV, and vice-versa. We discuss the likely mechanisms behind these differences which include: starburst ages, dust absorption, stellar energy ejecta through SNe and winds, as well as leakage of UV photons from stellar clusters. We conclude that the large scale morphological features in starbursts are primarily due to both age and absorption from a `picket fence' dust distribution. We further demonstrate the similarity and differences between these nearby starbursts and high redshift star forming galaxies. The overall morphology of our sample of starbursts changes little between UV and visible wavelengths. If high redshift galaxies are similar to these starbursts, their morphologies should change little between rest-frame UV and optical. We also show that FIR and UV spectral energy distributions and slopes can be used to determine large scale morphological features for extreme starbursts, with the steepest FIR slopes correlating with the most disturbed galaxies.

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arXiv1999

The NICMOS Snapshot Survey of nearby Galaxies

We present ``snapshot'' observations with the NearInfrared Camera and MultiObject Spectrometer (NICMOS) on board the Hubble Space Telescope (HST) of 94 nearby galaxies from the Revised Shapley Ames Catalog. Images with 0.2 as resolution were obtained in two filters, a broad-band continuum filter (F160W, roughly equivalent to the H-band) and a narrow band filter centered on the Paschen alpha line (F187N or F190N, depending on the galaxy redshift) with the 51x51 as field of view of the NICMOS camera 3. A first-order continuum subtraction is performed, and the resulting line maps and integrated Paschen alpha line fluxes are presented. A statistical analysis indicates that the average Paschen alpha surface brightness {\bf in the central regions} is highest in early-type (Sa-Sb) spirals.

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arXiv1999

Chemically Consistent Evolutionary Models with Dust

As a tool to interpret nearby and high redshift galaxy data from optical to K-band we present our chemically consistent spectrophotometric evolutionary synthesis models. These models take into account the increasing initial metallicity of successive stellar generations using recently published metallicity dependent stellar evolutionary tracks, stellar yields and model atmosphere spectra. The influence of the metallicity is analysed. Dust absorption is included on the basis of gas content and abundance as it varies with time and galaxy type. We compare our models with IUE template spectra and are able to predict UV fluxes for different spectral types. Combined with a cosmological model we obtain evolutionary and k-corrections for various galaxy types and show the differences to models using only solar metallicity input physics as a function of redshift, wavelength band and galaxy type.

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arXiv1999

The Structure and Morphology of the Ionized Gas in Starburst Galaxies: NGC5253/5236

(Abridged) We investigate the interplay between starbursts and host galaxies by studying the structure and physical characteristics of the ionized gas surrounding the central starbursts in the two nearby galaxies NGC5253 and NGC5236. The two systems represent very different galactic environments, NGC5253 being a metal-poor dwarf, and NGC5236 being a metal-rich, massive spiral. We present images of the starburst regions in these two galaxies in the line emission [OIII], H-alpha, and [SII], and in continuum U, V, R. For NGC5253, line ratio maps [OIII]/H-beta and [SII]/H-alpha show that in the outer regions the diffuse ionized gas (DIG) is partially excited by a non-photoionization process (`shocks'). The `shocked' gas is mostly concentrated south-west of the galaxy's center, in coincidence with the position of H-alpha bubbles and with extended soft X-ray emission. The H-alpha emission from the shock-excited gas is ~1-2% of the total. About 80-90% of the DIG is consistent with being photoionized, requiring that about 10% of the ionizing photons escape from the starburst site. The starburst in NGC5253 appears to be fed by gas infalling along the galaxy's optical minor axis, while hot gas expanding from the starburst has a preferential direction along the major axis. The results for NGC5236 are less clear than for NGC5253, as the images are not as deep. The emission line ratio maps show very little or no evidence for presence of shock excitation and very little or no ionized gas appears expanding from the center of the galaxy outward along the disk plane. The starburst in NGC5236 is thus more strongly confined than that in NGC5253, probably due to the deeper gravitational potential well of the more massive galaxy.

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arXiv1998

The Evolution of Dust Opacity in Galaxies

(Abridged) We investigate the evolution of the opacity of galaxies as a function of redshift, using simple assumptions about the metal and dust enrichment of the gas and the distribution of dust in galaxies. We use an iterative procedure to reconstruct the intrinsic Star Formation Rate (SFR) density of galaxies with redshift, by applying dust obscuration corrections to the observed UV emission. The iterative procedure converges to multiple solutions for the intrinsic SFR density, divided into two basic classes. The first class of solutions predicts relatively large UV attenuation at high redshift, with A(1500 A)=1.9 mag at z~3, and smaller attenuations at z<1, with A(2800 A)=1.25 mag. The SFR density of this set of solutions is constant for z>~1.2 and declines for z<1.2; it resembles in shape the ``monolithic collapse'' scenario for star formation. The second class of solutions predicts relatively low UV attenuations at high redshift, with A(1500 A)=0.75 mag at z~3, and larger attenuations at z<1, with A(2800 A)=1.50 mag. The SFR density in this case has a peak at z~1.2. The advantages and shortcomings of both classes are analyzed in the light of available observational constraints, including the opacity of galaxies at 0<z<1 and the intensity and spectral energy distribution of the cosmic infrared background from the COBE DIRBE and FIRAS data. We conclude that both classes of models are acceptable within the current uncertainties, but the ``monolithic collapse'' class matches the available observations better than the other one. We also investigate the dependence of our solutions on the different model assumptions.

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arXiv1997

Dust and Recent Star Formation in the Core of NGC5253

(Abridged) Ultraviolet and optical narrow and broad band images of NGC5253 obtained with the HST WFPC2 are used to derive the properties of the dust distribution and the recent star formation history of this metal-poor dwarf galaxy. Corrections for the effects of dust are important in the center of NGC5253: dust reddening is markedly inhomogeneous across the galaxy's central 20" region. One of the most obscured regions coincides with the region of highest star formation activity in the galaxy: clouds of more than 9~magnitudes of optical depth at V enshroud a young (2.5~Myr old) stellar cluster in the region. Star formation has been active at least over the past 100 Myr in the core of the galaxy, as indicated by the age distribution of both the blue diffuse stellar population and the bright stellar clusters. The star formation is currently concentrated in a 6" region, about 5 Myr old and with a star formation intensity 10-100 times higher than the average within the central 20". The 2.5 Myr old cluster coincides with the peak intensity of the star formation; its mass may be as large as 10^6 solar masses, making this one a Super-Star-Cluster candidate.

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arXiv1997

The Spectral Energy Distribution of Normal, Starburst and Active Galaxies

We present the results of an extensive literature search of multiwavelength data for a sample of 59 galaxies, consisting of 26 Starbursts, 15 Seyfert 2's, 5 LINER's, 6 normal spirals and 7 normal elliptical galaxies. The data include soft X-ray fluxes, ultraviolet and optical spectra, near, mid/far infrared photometry and radio measurements, selected to match as closely as possible the IUE aperture (10" X 20"). The galaxies are separated into 6 groups with similar characteristics, namely, Ellipticals, Spirals, LINER's, Seyfert 2's, Starbursts of Low and High reddening, for which we create average spectral energy distributions (SED). The individual groups SED's are normalized to the $λ$7000Åflux and compared, looking for similarities and differences among them.The bolometric fluxes of different types of galaxies were calculated integrating their SED's. These values are compared with individual waveband flux densities, in order to determine the wavebands which contribute most to the bolometric flux. Linear regressions were performed between the bolometric and individual band fluxes for each kind of galaxy. These fits can be used in the calculation of the bolometric flux for other objects of similar activity type, but with reduced waveband information. We have also collected multiwavelength data for 4 HII regions, a thermal supernova remnant, and a non-thermal supernova remnant (SNR), which are compared with the Starburst SED's.

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arXiv1997

Dust in Starburst Galaxies

To investigate the nature of starbursts' dust, we constructed a model of the stars and dust in starburst galaxies and applied it to 30 observed starburst spectral energy distributions (SEDs). The starburst model was constructed by combining two stellar evolutionary synthesis models with a model describing the radiative transfer of stellar photons through dust. The stellar evolutionary synthesis models were used to compute the dust-free SEDs for stellar populations with ages between 1x10^6 and 15x10^9 years. Using a Monte Carlo radiative transfer model, the effects of dust were computed for average Milky Way (MW) and Small Magellanic Cloud (SMC) dust, two different star/dust geometries, and locally homogeneous or clumpy dust. Using color-color plots, the starburst model was used to interpret the behavior of 30 starbursts with aperture-matched UV and optical SEDs (and IR for 19 of the 30) from previous studies. From the color-color plots, it was evident that the dust in starbursts has an extinction curve lacking a 2175 A bump, like the SMC curve, and a steep far-UV rise, intermediate between the MW and SMC curves. The star/dust geometry which is able to explain the distribution of the 30 starbursts in various color-color plots has an inner dust-free sphere of stars surrounded by an outer star-free shell of clumpy dust. When combined with other work from the literature on the Orion region and the 30 Dor region of the Large Magellanic Cloud, this work implies a trend in dust properties with star formation intensity.

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arXiv1994

Spectral Classification of Galaxies: An Orthogonal Approach

Classification of galaxy spectral energy distributions in terms of orthogonal basis functions provides an objective means of estimating the number of significant spectral components that comprise a particular galaxy type. We apply the Karhunen-Loève transform to derive a spectral eigensystem from a sample of ten galaxy spectral energy distributions. These spectra cover a wavelength range of 1200 Å to 1 $μ$m and galaxy morphologies from elliptical to starburst. We find that the distribution of spectral types can be fully described by the first two eigenvectors (or eigenspectra). The derived eigenbasis is affected by the normalization of the original spectral energy distributions. We investigate different normalization and weighting schemes, including weighting to the same bolometric magnitude and weighting by the observed distribution of morphological types. Projecting the spectral energy distributions on to their eigenspectra we find that the coefficients define a simple spectral classification scheme. The galaxy spectral types can then be described in terms of a one parameter family (the angle in the plane of the first two eigenvectors). We find a strong correlation in the mean between our spectral classifications and those determined from published morphological classifications.

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