We present the results of a Spitzer Infrared Spectrograph (IRS) survey of 24um-selected luminous infrared galaxies (LIRGs, L_IR > 10^11 L_sun) in the rich cluster Cl0024+16 at z=0.4. Optically, these LIRGs resemble unremarkable spiral galaxies with e(a)/e(c) spectral classifications and [Oii]-derived star formation rates (SFRs) of <2 M_sun/yr, generally indistinguishable from the 'quiescent' star forming population in the cluster. Our IRS spectra show that the majority of the 24um-detected galaxies exhibit polycyclic aromatic hydrocarbon (PAH) emission with implied SFRs ~30-60 M_sun/yr, with only one (<10%) of the sample displaying unambiguous evidence of an active galactic nucleus in the mid-infrared. This confirms the presence of a large population of obscured starburst galaxies in distant clusters, which comprise the bulk of the star formation occurring in these environments at z~0.5. We suggest that, although several mechanisms could be at play, these dusty starbursts could be the signature of an important evolutionary transition converting gas-rich spiral galaxies in distant clusters into the passive, bulge-dominated lenticular galaxies that become increasingly abundant in the cores of rich clusters in the ~4Gyr to the present day.
We present a new numerical code which is designed to derive a spectral energy distribution (SED) for an arbitrary spatial distribution of stellar and gaseous components in a dusty starburst galaxy. We apply a ray tracing method to numerical simulations and thereby estimate extinction and reemission of stellar light by dusty gas in an explicitly self-consistent manner. By using this code, we can investigate simultaneously dynamical and photometric evolution of a dusty galaxy based on stellar and gaseous dynamical simulations. As an example, we demonstrate when and how a major galaxy merger with…
By using a one-zone chemical and spectrophotometric evolution model of a disk galaxy undergoing a dusty starburst, we investigate, numerically, the optical spectroscopic properties in order to explore galaxy evolution in distant clusters. We adopt an assumption that the degree of dust extinction (represented by $A_V$) depends on the ages of starburst populations in such a way that younger stars have larger $A_V$ (originally referred to as selective dust extinction by Poggianti & Wu 2000). In particular, we investigate how the time evolution of the equivalent widths of [OII]$λ$3727 and H$δ$ is …
We present Spitzer Space Telescope observations of the well-studied extremely red objects (EROs) HR10 and LBDS53W091 from 3.6 to 160 microns. These galaxies are the prototypes of the two primary classes of EROs: dusty starbursts and old, evolved galaxies, respectively. Both galaxies, as well as LBDS53W069, another example of an old, quiescent galaxy, are well-detected out to 8 microns. However, only the dusty starburst HR10 is detected in the far-infrared. All three EROs have stellar masses of a few times 10^11 M(sun). Using evolutionary model fits to their multiband photometry, we predict the…
The 2 Ms Chandra Deep Field-North survey provides the deepest view of the Universe in the 0.5--8.0 keV X-ray band. In this brief review we investigate the diversity of X-ray selected sources and focus on the constraints placed on AGNs (including binary AGNs) in high-redshift submm galaxies.
The formation and evolution of the ``E+A'' (also named ``k+a'' and ``a+k'' types by Dressler et al. 1999) galaxies found in significant numbers in the cores of intermediate redshift clusters has been extensively discussed by many authors. In this paper, we model the spectral, dynamical and morphological evolution of a prime candidate for producing this spectral signature: a dusty starburst associated with a major galaxy merger. We show that as this system evolves dynamically, its spectral type changes from and ``e(a)'' type (exhibiting strong H$δ$ absorption and modest [OII] emission -- the id…
By performing N-body simulations of chemodynamical evolution of galaxies with dusty starbursts, we investigate photometric evolution of gas-rich major mergers in order to explore the nature of ultraluminous infrared galaxies (ULIRGs) with the total infrared luminosity ($L_{\rm IR}$ for $8\sim 1000$ $μ$m) of $\sim$ $10^{12}$ $L_{\odot}$. Main results are the following three. (1) Global colors and absolute magnitudes the during dusty starburst of a major merger do not change with time significantly, because interstellar dust heavily obscures young starburst populations that could cause rapid evo…
E+A galaxies are characterized as a galaxy with strong Balmer absorption lines but without any [OII] or Halpha emission lines. Strong Balmer absorption lines indicate that E+A galaxies have experienced a starburst within the last <1-1.5 Gyr. However, the lack of emission lines indicates that E+A galaxies do not have any on-going star formation. Therefore, E+A galaxies are interpreted as a post-starburst galaxy. However, it has been a mystery why E+A galaxies underwent a starburst then stopped abruptly. One possible explanation to E+A galaxies is the dusty starburst scenario, where E+A galaxies…
This contribution presents the optical spectral properties of FIR-luminous galaxies, whose distinctive feature is often the simultaneous presence in the spectra of a strong $\rm Hδ$ line in absorption and of emission lines (e(a) spectra). A discrepancy between the star formation rate estimated from the FIR luminosity and that derived from the $\rm Hα$ luminosity persists even after having corrected the $\rm Hα$ flux for dust according to the observed Balmer decrement. It is shown that the e(a) spectrum can be reproduced assuming a current starburst and dust extinction affecting the youngest st…
We have measured central line strengths for a complete sample of early type galaxies in the Fornax cluster, comprising 11 elliptical and 11 lenticular galaxies, more luminous than M_B=-17. In contrast to the elliptical galaxies in the sample studied by Gonzalez (and recently revisited by Trager) we find that the Fornax ellipticals follow the locus of galaxies of fixed age in Worthey's models and have metallicities varying from roughly solar to three times solar. The lenticular galaxies however exhibit a substantial spread to younger luminosity weighted ages indicating a more extended star form…
Dusty starbursts were more numerous around z~1 than today and appear to be responsible for the majority of cosmic star formation over the Hubble time. We suggest that they represent a common phase within galaxies in general which is triggered by the growth of cosmic structure. We discuss the origin of the luminosity of luminous infrared galaxies at z~1. Are these galaxies dominated by star formation or nuclear activity ? What is triggering their strong activity ? Is it triggered by external interactions or did it happen naturally within isolated galaxies ? We present HST-ACS high resolution op…
We consider the radiation-hydrodynamical formation of a dusty wall in the circumnuclear regions of the Circinus Seyfert 2 galaxy. We focus on the radiative flux force due to the circumnuclear starburst, the nuclear starburst and the active galactic nucleus (AGN), and analyze the equilibrium configuration and stability of the dusty gas in the circumnuclear regions. The mass distributions used to model the gravitational fields are determined by the observed rotation velocities of the stars and of the gas. Moreover, by using the simple stellar evolution in the circumnuclear starburst, the bolomet…
As a logical next step in improving the radio-to-submm spectral index as a redshift indicator (Carilli & Yun 1999), we have investigated a technique of using the entire radio-to-FIR spectral energy distribution (SED) for deriving photometric redshifts for dusty starburst galaxies at high redshift. A dusty starburst SED template is developed from theoretical understanding on various emission mechanisms related to massive star formation process, and the template parameters are selected by examining the observed properties of 23 IR selected starburst galaxies: $T_d=58$ K, $β=1.35$, and $f_{nth}=1…
Using the IRAM Plateau de Bure Interferometer, we have searched for CO(3-2) emission from the dusty Lyman break galaxy Westphal-MD11 at z = 2.98. Our sensitive upper limit is surprisingly low relative to the system's 850 um flux density and implies a far-IR/CO luminosity ratio as elevated as those seen in local ultraluminous mergers. We conclude that the observed dust emission must originate in a compact structure radiating near its blackbody limit and that a relatively modest molecular gas reservoir must be fuelling an intense nuclear starburst (and/or deeply buried active nucleus) that may h…
We report observational analyses and theoretical interpretations of unusually red galaxies in the Subaru Deep Field (SDF). A careful analysis of the SDF data revealed a population with unusually red near-infrared (NIR) colors of J - K >~ 3-4, with higher confidence than the previous SDF result. Their surface number density drastically increases at K >~ 22 and becomes roughly the same with that of dusty starburst galaxies detected by submillimeter observations in recent years. These colors are even redder than the known population of the extremely red objects (EROs), and too red to explain by p…
Understanding the origin of stellar masses is a key problem in astrophysics. In the solar neighborhood, the mass distribution of stars follows a seemingly universal pattern. In the centre of the Milky Way, however, there are indications for strong deviations and the same may be true for the nuclei of distant starburst galaxies. Here we present the first numerical hydrodynamical calculations of stars formed in a molecular region with chemical and thermodynamic properties similar to those of warm and dusty circum-nuclear starburst regions. The resulting IMF is top-heavy with a peak at ~ 15 Msun,…
We present near-IR spectroscopy and HST imaging of EROJ164023, an Extremely Red Object (ERO) with R-K=5.9 at z=1.05. EROJ164023 is a disk galaxy, with an optical/IR spectral energy distribution which is strongly reddened by dust (L_FIR/L_B<~200; A_V~5). The narrow emission lines (~300km/s) and the high [NII]/Halpha line ratio indicate that this is a ``composite'' starburst-Seyfert galaxy. Assuming that star formation dominates, we constrain the SFR to be 10-700Mo/yr from a variety of indicators. We compare EROJ164023 with the only other spectroscopically identified dusty EROs: HR10 (z=1.44) an…
We model the constraints set on the evolution of dusty starburst galaxies by the current deep extragalactic surveys performed in the far-infrared with $\it Spitzer$, and at radio wavelengths with the VLA. Our models fit the number counts in all the available spectral bands well, and also provide a reasonably close match to the redshift distribution of the $\it Spitzer$ detections. We find: 1.) dusty starburst galaxies with infrared burst phases triggered by galactic interactions at redshift $z \sim 1-2$ are good candidates to fit the $\it Spitzer$ results at $24μm$, $70 μm$ and $160 μm$, assum…
We report the detection of the Diffuse Interstellar Bands (``$DIBs$'') in the optical spectra of seven far-infrared-selected starburst galaxies. The $λ$6283.9 Åand $λ$ 5780.5 Åfeatures are detected with equivalent widths of $\sim$ 0.4 to 1 Åand 0.1 to 0.6 Årespectively. In the two starbursts with the highest quality spectra (M82 and NGC2146), four other weaker $DIBs$ at $λ$ 5797.0 Å, 6010.1 Å, 6203.1 Å, and 6613.6 Åare detected with equivalent widths of $\sim$ 0.1 Å. The region over which the $DIBs$ can be detected ranges from $\sim$ 1 kpc in the less powerful starbursts, to several kpc in the…
Recent observational studies on galaxies in distant clusters discovered a significant fraction of possible dusty starburst galaxies with the so-called `e(a)' spectra that are characterized by strong H$δ$ absorption and relatively modest [OII] emission. We numerically investigate spectroscopic and photometric evolution of dusty starburst galaxies in order to clarify the origin of the e(a) spectra. We found that if a young starburst population is preferentially obscured by dust than an old one in a dusty starburst galaxy, the galaxy shows e(a) spectrum. It is therefore confirmed that the selecti…
By using a new numerical code for deriving the spectral energy distributions of galaxies, we have investigated the time evolution of morphological properties, the star formation rate, and the submillimeter flux at 850 $μ$m in high-redshift ($z$) dusty starburst mergers with mass ratio ($m_{2}$) of two disks ranging from 0.1 (minor merger) to 1.0 (major one). We found that the maximum star-formation rate, the degree of dust extinction, and the 850 $μ$m flux are larger for mergers with larger $m_{2}$. The 850 $μ$m flux from mergers at 1.5 $\le z \le$ 3.0 in the observer frame is found to be a fe…
Star formation rates in galaxies are frequently estimated using the Balmer line fluxes. However, these can be systematically underestimated because dust competes for the absorption of Lyman continuum photons in the ionized gas. Here we present theoretical correction factors in a simple analytic form. T These factors scale as the product of the ionization parameter, ${\cal U}$, and the nebular O/H abundance ratio, both of which can now be derived from the observation of bright nebular line ratios. The correction factors are only somewhat dependent upon the photoelectron production by grains, bu…
We have thoroughly characterized the ultraviolet to near-infrared (0.15 - 2.2 micron) spectral energy distribution (SED) of the central parsec of the M33 nucleus through new infrared photometry and optical/near-infrared spectroscopy, combined with ultraviolet/optical observations from the literature and the HST archive. The SED shows evidence for a significant level of attenuation, which we model through a Monte Carlo radiative transfer code as a shell of clumpy Milky Way-type dust (tau_V ~ 2 +/- 1). The discovery of Milky Way-type dust (with a strong 2175 A bump) internal to the M33 nucleus i…
An evolutionary model of star formation in ULIRGs was created using existing star formation and radiative transfer codes (STARBURST99, RADMC and RADICAL) as building blocks. The results of the simulations are compared to data from two IRAS catalogs. From the simulations it is found that the dust surrounding the starburst region is made up from two components. There is a low optical depth (tau=0.1, which corresponds to 0.1% of the total dust mass), hot (T~400K) non-grey component close to the starburst (scale size 10pc) and a large scale, colder grey component (100pc, 75K) with a much larger co…
We revisit the nature of the FIR/Radio correlation by means of the most recent models for star forming galaxies. We model the IR emission with our population synthesis code, GRASIL (Silva et al. 1998). As for the radio emission, we revisit the simple model of Condon & Yin (1990). We find that a tightFIR/Radio correlation is natural when the synchrotron mechanism dominates over the inverse Compton, and the electrons cooling time is shorter than the fading time of the supernova rate. Observations indicate that both these conditions are met in star forming galaxies. However since the radio non th…
We develop and apply a dual-survey extraction technique to published submm images of the Lockman Hole using the SCUBA and MAMBO bolometer arrays. Cut above 5 sigma, this catalogue of submm galaxies (SMGs) is significantly more robust than previous samples, typically selected above 3.0-3.5 sigma, with a much-reduced likelihood of real, faint SMGs (beneath and around the confusion limit) entering the catalogue via superposition with noise. Our selection technique yields 19 SMGs of which we expect at most two to be due to chance superposition of SCUBA and MAMBO noise peaks. The flux limit of the …
We present a sample of mid-infrared detected sources from the European Large Area ISO Survey (ELAIS) regions characterised by strong mid-IR radiation with faint near-IR and optical counterparts. These extreme mid-to-near-IR objects (EMNOs) are defined here by a flux ratio of f_15um / f_2.2um > 25. This population is not obvious in deeper small area ISO surveys, though it produces more than 20% of the observed cosmic IR background radiation (CIRB) at 15um above 1 mJy. Near-future large area deep mid-IR surveys with the Spitzer Space Telescope, however, are bound to uncover large amounts of thes…
At a conference devoted to ever deeper surveys hunting for ever more distant galaxies, I posed a question for which a concensus view has been difficult to reach: `Is there evidence for, or can we rule out, a significant population of dust-obscured starbursts at z > 3?' If, as seems likely, submm-selected galaxies are proto-ellipticals, one of the biggest unanswered questions is whether a significant fraction form at very high redshift - perhaps by the collapse of single gas clouds - or whether the entire population forms over a range of redshifts, primarily via merging. The latter scenario is …
We analyse the optical spectral properties of the complete sample of Very Luminous Infrared Galaxies presented by Wu et al. (1998a,b) and we find a high fraction (~50 %) of spectra showing both a strong H_delta line in absorption and relatively modest [OII] emission (e(a) spectra). The e(a) signature has been proposed as an efficient method to identify dusty starburst galaxies and we study the star formation activity and the nature of these galaxies, as well as the effects of dust on their observed properties. We examine their emission line characteristics, in particular their [OII]/H_alpha ra…
We present ISO mid-infrared spectrophotometry and far-infrared photometry of galaxies with Hidden Broad Line Regions (HBLR). We also present radiative transfer models of their spectral energy distributions which enable us to separate the contributions from the dusty disc of the AGN and the dusty starbursts. We find that the combination of tapered discs (discs whose thickness increases with distance from the central source in the inner part but stays constant in the outer part) and starbursts provide good fits to the data. The tapered discs dominate in the mid-infrared part of the spectrum and …
Aims: We aim at detecting and determining the properties of the host galaxy of the dark GRB 050223. Methods: We use VLT optical/NIR images coupled to Swift X-ray positioning, and optical spectra of the host galaxy to measure its properties. Results: We find a single galaxy within the Swift error box of GRB 050223. It is located at z = 0.584 and its luminosity is L ~ 0.4 L*. Emission lines in the galaxy spectrum imply an intrinsic SFR > 7 Msun/yr, and a large extinction A_V > 2 mag within it. We also detect absorption lines, which reveal an underlying stellar population with an age between 40 M…
We re-address the classification criterion for extremely red galaxies (ERGs) of Pozzetti and Mannucci (2000 -- PM00), which aims to separate, in the Ic-K (or Rc-K) vs. J-K colour--colour diagram, passively evolving, old (> 1 Gyr) stellar populations in a dust-free environment, associated with ellipticals (Es), from dusty starburst galaxies (DSGs), both at 1 < z < 2. We explore a category of objects not considered previously, i.e., galaxies forming in this redshift range on short (0.1 Gyr) timescales and observed also in their early, dusty post-starburst phase. We also investigate the impact of…
We present an analysis of the emission line property and the broad band spectral energy distribution of the ultra-luminous infrared Type II quasar Q132+058. The optical and ultraviolet emission lines show four distinct components: a LINER-like component at the systematic velocity, a heavily reddened HII-like component blueshifted by about 400 km/s, and two broad components blueshifted by about 400 km/s and 1900 km/s, respectively. The emission line ratios suggest that broad components are produced in dense and alpha-enriched outflows with a metalicity of 3-5 Zsun and a density of n_H ~ 10^7 cm…
To better understand the early stages of massive star cluster evolution we have obtained J,H,K', and N (10.8 micron) images of the nuclear region of the starburst galaxy He 2-10. The N-band images were obtained with the Gemini North telescope and reveal four of the five enshrouded clusters, or "ultradense HII regions" (UDHIIs), recently discovered in radio maps. None of these sources appears in either the optical HST images or the near-infrared images. They comprise about 60% of the total N-band flux from He 2-10 and, we suspect, a similar fraction of the total far infrared flux measured by IR…
We report on infrared K- (2-2.5 micron) and L-band (2.8-4.1 micron) slit spectroscopy of 23 Seyfert 1 galaxies in the CfA and 12 micron samples. A polycyclic aromatic hydrocarbon (PAH) emission feature at 3.3 micron in the L band is primarily used to investigate nuclear star-forming activity in these galaxies. The 3.3 micron PAH emission is detected in 10 sources (=43%), demonstrating that detection of nuclear star-formation in a significant fraction of Seyfert 1 galaxies is now feasible. For the PAH-detected nuclei, the surface brightness values of the PAH emission are as high as those of typ…
Phenomenological models for evolution of dusty galaxies and E/S0 galaxies, respectively, are developed to address two major questions concenring galaxy populations in deep infrared (IR) surveys: (1) Do normal late-type galaxies or starburst galaxies (including galaxies with obscured AGNs) dominate among sources in deep IR surveys? (2) How much do E/S0 galaxies contribute to the counts in deep mid-infrared (MIR: 3 -- 20$μm$) surveys? Among three new models for evolution of dusty galaxies, it is assumed in Model S1 that starburst galaxies are the dominant population, and in Model S2 that normal …
The infrared regime contains a number of unique diagnostic features for probing the astrophysics of starburst galaxies. After a brief summary of the most important tracers, we focus in detail on the use of emission lines to probe the upper part of the main sequence in a young superstarcluster in the Antennae, and the compact, dusty starburst in the nucleus of the nearby ultraluminous infrared galaxy Arp220
We present results of Monte Carlo calculations for the Lya line transfer in an expanding dusty supershell, where Lya source is a well-localized star cluster in a starburst galaxy.The escape of Lya photons from such system is achieved by a number of back-scattering, and so a series of emission peaks are formed redward of the systemic redshift by back-scattering. However, majority of observed Lya emission from starbursts show singly-peaked asymmetric profiles. We find in this paper that, in order to form a singly-peaked Lya emission, dust should be distributed in the ionized bubble, as well as w…
We present deep Hubble Space Telescope and Spitzer Space Telescope observations of the host galaxy of GRB 050904 at z=6.295. The host is detected in the H-band and marginally at 3.6 micron. From these detections, and limits in the z'-band and 4.5 micron, we infer an extinction-corrected absolute magnitude, M(UV)=-20.7 mag, or ~L*, a substantial star formation rate of 15 solar masses per year, and a stellar mass of a few 10^9 solar masses. A comparison to the published sample of spectroscopically-confirmed galaxies at z>5.5 reveals that the host of GRB 050904 would evade detection and/or confir…
We investigate when and how a dusty starburst galaxy merger can be heavily obscured by dust and consequently becomes an ultra-luminous infrared galaxy (ULIRG), based on numerical simulations of chemodynamical and photometric evolution of dusty gas-rich major galaxy mergers. We found that a major galaxy merger is more likely to become an ULIRG preferentially in the merger late phase, when the two disks become very close and the very high-density dusty gas can obscure heavily the central secondary massive starburst. We furthermore show how the optical and near-infrared morphology of a simulated …
The modest significance of most sources detected in current submm surveys can potentially compromise some analyses due to the inclusion of spurious sources in catalogues typically selected at >3.0-3.5sigma. Here, we develop and apply a dual-survey extraction technique to SCUBA and MAMBO images of the Lockman Hole. Cut above 5sigma, our catalogue of SMGs is more robust than previous samples, with a reduced likelihood of real, but faint SMGs (beneath and around the confusion limit) entering via superposition with noise. The effective flux limit of the survey is well matched to our deep 1.4-GHz i…
We determine the nature, redshift, stellar populations and dust properties of optically faint or non-detected extremely red objects (ERO) found from our survey of the lensing clusters A1835 and AC114. We perform SED fitting and use deep optical, HST, VLT, Spitzer data, and for some objects and sub-mm data. For most of the lensed EROs we find photometric redshifts showing a strong degeneracy between "low-z" (z~1-3) and high-z (z~6-7). Although formally best fits are often found at high-z, their resulting bright absolute magnitudes, the number density of these objects, and in some cases Spitzer …
We present a method based on two broad-band colors to investigate the nature of the Extremely Red Objects (EROs), i.e., the galaxies selected to have very red optical-to-infrared colors. Dusty starburst and old ellipticals at redshifts between 1 and 2 appear to occupy two different regions of the J-K vs. I-K color diagram, allowing for an easy classification. This diagnostic was applied to a complete sample of 57 EROs: the two populations are found to be present in the sample in similar abundances. The cosmic star formation density in the dusty starbursts is found to be of the order of that in…
Radio galaxies characteristically have strong Lya emission lines. However, a few have Lya equivalent widths that are substantially weaker in relation to other emission lines. One in particular was studied by Dey etal (1995), MG 1019+0535 (z=2.765). We report on our reduction of Infrared Space Observatory (ISO}) data in the 160 micron-band for this galaxy. We also compile information on two other high redshift active galaxies with weak Lya lines, the radio galaxy TXS 0211-122, and the AGN-starburst galaxy F 10214+4724, to provide a small weak-Lya line sample. IRAS plus ISO data show that F 1021…
We present J band observations of a complete sample of 57 red galaxies selected to have K<20 and R-K>5.3. We use the Pozzetti and Mannucci (2000) prescriptions, based on the R-K and J-K colours, to separate the two dominant populations, old ellipticals and dusty starbursts. We find that both populations are present in the current sample and have similar abundances, and discuss the uncertainties in this result. Galactic stars comprise about 9% of the objects. The starburst galaxies of the present sample are found to give a contribution to the cosmic star formation density similar to the Lyman-b…
We present infrared 2.8-4.1 micron slit spectra of 32 Seyfert 2 galaxies in the CfA and 12 micron samples. The 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission feature was used to estimate the absolute magnitude of a compact nuclear starburst (< a few 100 pc in size) that is presumed to have occurred in the outer region of an obscuring dusty molecular torus around a central supermassive black hole. We detected 3.3 micron PAH emission in 11 of the 32 Seyfert 2 nuclei in our sample, providing evidence for the presence of compact nuclear starbursts in a significant fraction of Seyfert 2 …
We present absorption line strength maps of 48 representative elliptical and lenticular galaxies obtained as part of the SAURON survey of nearby galaxies. Using high-quality spectra, spatially binned to a constant signal-to-noise, we measure four key age, metallicity and abundance ratio sensitive indices from the Lick/IDS system over a two-dimensional field extending up to approximately one effective radius. We modify the classical Fe5270 index to define a new index, Fe5270S, which maximizes the usable spatial coverage of SAURON. Maps of Hbeta, Fe5015, Mgb and Fe5270S are presented for each ga…
Near infrared (NIR) and optical surface photometric analyses of the dusty galaxy NGC972 are presented. The photometric profiles in the BVRJHK bands can be fitted with a combination of gaussian and exponential profiles, corresponding to a starburst nucleus and a stellar disk respectively. The exponential scale length in the B-band is 2.8 times larger than in the K-band, which implies a central B-band optical depth as high as 11. A bulge is absent even in the NIR bands and hence the galaxy must be of a morphological type later than the usually adopted Sb type. Relatively low rotational velocity …
We present HST (WFPC2 and FOC) images and UV GHRS spectra plus ground-based optical spectra of four Luminous Infrared Galaxies (LIRGs) that have Seyfert 2 nuclei (Mrk 477, NGC 7130, NGC 5135 and IC 3639). The data provide direct evidence of the existence of a central nuclear starburst that dominates the UV and optical light and are dusty and compact. The bolometric luminosity of 10$^{10}$ Lsol of these starbursts is similar to the estimated bolometric luminosities of their obscured Seyfert 1 nuclei, and thus they contribute in the same amount to the overall energetics of these galaxies. An ext…
We report on the environments, kinematics, and SFH of [OII]-selected objects in the z=0.4 galaxy cluster A851, using Keck optical spectra. A large fraction (~55%) of cluster [OII] emitters show strong Balmer absorptions (>4A in equivalent width at Hd). These e(a) spectra have been attributed to dusty starburst galaxies, an interpretation supported by our reddening measurements, which show a high frequency of very reddened [EBV>0.5] [OII] emitters. Our spectral modeling requires starburst ages >1Gyr, shorter than the cluster crossing timescale. We argue that this starburst phase occurs during c…
We report evidence for a recent burst of star formation located within 9 pc of the active nucleus of NGC 1097. The observational signatures of the starburst include UV absorption lines and continuum emission from young stars observed in a small-aperture HST spectrum. The burst is a few times 10^6 yr old, has a mass of approximately 10^6 solar masses, an observed luminosity of 1.5 x 10^7 solar luminosities and is obscured by approximately 3 visual magnitudes. The importance of this finding is two-fold: (1) the proximity of the starburst to the active nucleus and thus possible association with i…
Far-infrared flux densities are newly extracted from the IRAS database for the RSA and CfA complete samples of Seyfert galaxies. These data are used to classify the Seyfert galaxies into those where the far-infrared continuum emission is dominated by the active galactic nucleus (AGN), circumnuclear starburst, or host galaxy. While AGN-dominant objects consist of comparable numbers of Seyfert 1 and 2 galaxies, starburst- and host-dominant objects consist preferentially of Seyfert 2 galaxies. Thus, in addition to the dusty torus, the circumnuclear starburst region and host galaxy are important i…
We present a new multi-component spectral energy distribution (SED) decomposition method and use it to analyze the ultraviolet to millimeter wavelength SEDs of a sample of dusty infrared-luminous galaxies. SEDs are constructed from spectroscopic and photometric data obtained with the Spitzer Space Telescope, in conjunction with photometry from the literature. Each SED is decomposed into emission from populations of stars, an AGN accretion disk, PAHs, atomic and molecular lines, and distributions of graphite and silicate grains. Decompositions of the SEDs of the template starburst galaxies NGC7…
Dusty galaxies with luminosities in excess of 10^11 solar luminosities have been detected out to redshifts of about unity by the Infrared Space Observatory (ISO), and to higher redshifts using millimetre(mm)- and submm-wave cameras on ground-based telescopes. The integrated properties of these more distant galaxies are also constrained by measurements of the intensity of the submm-wave background radiation. While it is generally unclear whether their energy is released by gravitational accretion or by star formation, circumstantial evidence favours star formation. Unless these high-redshift ga…
Low-ionization broad absorption line (BAL) QSOs present properties that cannot generally be explained by simple orientation effects. We have conducted a deep spectroscopic and imaging study of the host galaxies of the only four BAL QSOs that are currently known at z < 0.4, and found that all four objects reside in dusty, starburst or post-starburst, merging systems. The starburst ages derived from modeling the stellar populations are in every case a few hundred million years or younger. There is strong evidence that the ongoing mergers triggered both the starbursts and the nuclear activity, th…
The luminosity of the central source in ionizing radiation is an essential parameter in a photoionized environment, and one of the most fundamental physical quantities one can measure. We outline a method of determining luminosity for any emission-line region using only infrared data. In dusty environments, grains compete with hydrogen in absorbing continuum radiation. Grains produce infrared emission, and hydrogen produces recombination lines. We have computed a very large variety of photoionization models, using ranges of abundances, grain mixtures, ionizing continua, densities, and ionizati…
The empirical reddening function for starburst galaxies generated by Calzetti and her co-workers has proven very successful, and is now used widely in the observational literature. Despite its success, however, the physical basis for this extinction law, or more correctly, attenuation law remains weak. Here we provide a physical explanation for the Calzetti Law based on a turbulent interstellar medium. In essence, this provides a log-normal distribution of column densities, giving a wide range of column densities in the dusty foreground screen. Therefore, extended sources such as starburst reg…
We derive the properties of dusty tori in Active Galactic Nuclei (AGN) from the comparison of observed Spectral Energy Distributions (SEDs) of SDSS quasars and a precomputed grid of torus models. The observed SEDs comprise SDSS photometry, 2MASS J, H, and K data, whenever available and mid-Infrared (MIR) data from the Spitzer Wide-area InfraRed Extragalactic (SWIRE) Survey. The adopted model is that of Fritz et al., 2006. The fit is performed by standard chi^2 minimisation, the model however can be multi-component comprising a stellar and a starburst components, whenever necessary. Models with…
We present evolutionary synthesis models for galaxies of spectral types Sa through Sd with starbursts of various strengths triggered at various redshifts and study their photometric evolution before, during, and after their bursts in a cosmological context. We find that bursts at high redshift, even very strong ones, only cause a small blueing of their intrinsically blue young parent galaxies. At lower redshift, even small bursts cause a significant blueing of their intrinsically redder galaxies. While the burst phase is generally short, typically a few hundred Myr in normal-mass galaxies, the…
We perform UBR imaging and optical spectroscopy of the interacting galaxy pair Arp 104, at z=0.0098. This consists of NGC5218, a disturbed Sb barred spiral with an inclined outer shell, the round spheroidal NGC5216, a connecting bridge of length 50 kpc and a curved plume. Neither galaxy shows emission lines. NGC5218 has strong Balmer lines and appears to have undergone a major starburst some 0.2 Gyr ago, triggered by the last close passage of the two galaxies. The galaxy is very red in its centre, suggesting it is dusty, but its outer regions, and the bridge connecting the two galaxies, have t…
We investigate the star formation and dust extinction properties of very luminous infrared galaxies whose spectra display a strong Hdelta line in absorption and a moderate [OII] emission (e[a] spectrum). This spectral combination has been suggested to be a useful method to identify dusty starburst galaxies at any redshift on the basis of optical data alone. We compare the average e(a) optical spectrum with synthetic spectra that include both the stellar and the nebular contribution, allowing dust extinction to affect differentially the stellar populations of different ages. We find that reprod…
