Starburst Nucleus Galaxies Research Articles

Cosmic-ray induced ionization rates and non-thermal emissions from nuclei of starburst galaxies

ABSTRACT Cosmic rays are the only agent capable of ionizing the interior of dense molecular clouds and, thus, they are believed to play an essential role in determining the physical and chemical evolution of star-forming regions. In this work, we aim to study cosmic-ray induced ionization rates in starburst environments using non-thermal emissions of cosmic rays from starburst nuclei. To this end, we first revisit cosmic-ray models, which could explain data of non-thermal emissions from radio to X-ray and gamma-ray from nuclei of three prototypical starburst galaxies NGC 253, M82, and Arp 220. These models are then applied to predict ionization rates in starburst environments, which gives values around 10−14 s−1. Such a high value of the ionization rate, which is 2 to 3 orders of magnitude higher than the typical values found in the Milky Way, is probably due to relatively high rates of supernova explosions occurring within the nuclei of these starburst galaxies. We also discuss in more detail the case of NGC 253, where our predicted ionization rate is found to be, in most cases, a few times smaller than the values inferred from molecular line observations of clouds in the starburst nucleus. The general framework provided in this work illustrates how the use of non-thermal emission data could help to provide more insights into ionization rates or, more generally, cosmic-ray impact in starburst environments.

Contribution of starburst nuclei to the diffuse gamma-ray and neutrino flux

ABSTRACT In nuclei of starburst galaxies (SBGs), the combination of an enhanced rate of supernova explosions and a high gas density suggests that cosmic rays (CRs) can be efficiently produced, and that most of them lose their energy before escaping these regions, resulting in a large flux of secondary products, including neutrinos. Although the flux inferred from an individual starburst region is expected to be well below the sensitivity of current neutrino telescopes, such sources may provide a substantial contribution to the diffuse neutrino flux measured by IceCube. Here, we compute the gamma-ray and neutrino flux due to SBGs based on a physical model of CR transport in a starburst nucleus, and accounting for the redshift evolution of the number density of starburst sources as inferred from recent measurements of the star formation rate. The model accounts for gamma-ray absorption both inside the sources and in the intergalactic medium. The latter process is responsible for electromagnetic cascades, which also contribute to the diffuse gamma-ray background at lower energies. The conditions for acceleration of CR protons up to energies exceeding $\sim 10 \, \rm PeV$ in starburst regions, necessary for the production of PeV neutrinos, are investigated in a critical way. We show that starburst nuclei can account for the diffuse neutrino flux above $\sim 200 \, \rm TeV$, thereby producing $\lesssim 40 {\rm { per\, cent}}$ of the extragalactic diffuse gamma-ray background. Below $\sim 200 \, \rm TeV$, the flux from starburst appears to be somewhat lower than the observed one, where both the Galactic contribution and the flux of atmospheric neutrinos may account for the difference.

Cosmic ray transport and radiative processes in nuclei of starburst galaxies

AbstractThe high rate of star formation and supernova explosions of starburst galaxies make them interesting sources of high-energy radiation. Depending on the level of turbulence present in their interstellar medium, the bulk of cosmic rays produced inside starburst galaxies may lose most of their energy before escaping, thereby making these sources behave as calorimeters, at least up to some maximum energy. Contrary to previous studies, here we investigate in detail the conditions under which cosmic ray confinement may be effective for electrons and nuclei and we study the implications of cosmic ray confinement in terms of multifrequency emission from starburst nuclei and production of high-energy neutrinos. The general predictions are then specialized to three cases of active starbursts, namely, M82, NGC 253, and Arp220. Both primary and secondary electrons, as well as electron–positron pairs produced by gamma-ray absorption inside starburst galaxies are taken into account. Electrons and positrons produced as secondary products of hadronic interactions are found to be responsible for most of the emission of leptonic origin. In particular, synchrotron emission of very high energy secondary electrons produces an extended emission of hard X-rays that represents a very interesting signature of hadronic process in starburst galaxies, potentially accessible to current and future observations in the X-ray band. A careful understanding of both the production and absorption of gamma-rays in starburst galaxies is instrumental to the assessment of the role of these astrophysical sources as sources of high-energy astrophysical neutrinos.

MID-INFRARED POLYCYCLIC AROMATIC HYDROCARBON AND H 2 EMISSION AS A PROBE OF PHYSICAL CONDITIONS IN EXTREME PHOTODISSOCIATION REGIONS

Mid-infrared (IR) observations of polycyclic aromatic hydrocarbons (PAHs) and molecular hydrogen emission are a potentially powerful tool to derive physical properties of dense environments irradiated by intense UV fields. We present new, spatially resolved, \emph{Spitzer} mid-IR spectroscopy of the high UV-field and dense photodissocation region (PDR) around Monoceros R2, the closest ultracompact \hII region, revealing the spatial structure of ionized gas, PAHs and H$_2$ emissions. Using a PDR model and PAH emission feature fitting algorithm, we build a comprehensive picture of the physical conditions prevailing in the region. We show that the combination of the measurement of PAH ionization fraction and of the ratio between the H$_2$ 0-0 S(3) and S(2) line intensities, respectively at 9.7 and 12.3 $\mu$m, allows to derive the fundamental parameters driving the PDR: temperature, density and UV radiation field when they fall in the ranges $T = 250-1500 $K, $n_H=10^4-10^6$cm$^{-3}$, $G_0=10^3-10^5$ respectively. These mid-IR spectral tracers thus provide a tool to probe the similar but unresolved UV-illuminated surface of protoplanetary disks or the nuclei of starburst galaxies.

ISO observations of the Galactic center interstellar medium

We present fine structure and recombination line observations of the ionized gas toward a sample of 18 sources located within 300 pc of the center of the Galaxy (hereafter Galactic center, GC). The sources were selected as molecular clouds located far from thermal continuum sources. The fine structure lines from [Nii] and [Siii] were detected in 16 sources. In 10 sources we even detected the [Oiii] 88 μm line. Several techniques have been used to determine lower and upper limits to the extinction toward each source to correct the observed line fluxes. The derived electron densities of the ionized gas vary from ~100 to ≤30 cm-3. For some sources we were able to derive N, S and Ne abundances. We found that they are similar to those measured in the Hii regions in the 5-kpc ring and in the nuclei of starburst galaxies. The fine structure lines ratios measured for all the sources can be explained by photo-ionization with an effective temperature of the ionizing radiation of 32 000-37 000 K and an ionization parameter, U, of . The highest excitation is found in the Radio Arc region but it does not decrease smoothly with distance. There must be more ionizing sources distributed over the Galactic center than the known clusters of massive stars. Most of the clouds are located far (up to 45 pc for M-0.96+0.13) from the prominent continuum complexes (Sgr C, B ...). However, it is possible that the clouds are ionized by escaped photons from those complexes. The comparison of the effective temperatures of the ionizing radiation to the measured Lyman continuum photon emission rate implies that the clouds are indeed ionized by distant sources. The excitation ratios, effective temperature and ionization parameter measured in the GC are similar to those found in some low excitation starburst galaxies. The [Neiii]/[Neii] line ratios measured in the GC sources are consistent with the results of the Thornely et al. (2000) model for a short burst of massive star formation less than 8 Myr ago. We have also found that the [Neii] 13 μm to far-infrared continuum ratio measured for the GC sources is similar to that of external galaxies, supporting the idea of Sturm et al. ([CITE]) that the far-infrared continuum in Active Galaxies is dominated by dust heated by stellar radiation rather than by the AGN.

Abundances ratios in star-forming galaxies: clues to galaxy evolution

We show in this contribution that detailed studies of chemical abundances in UV-selected, H ii and starburst nucleus galaxies, together with the development of new chemical evolution models, put strong constraints on the evolutionary stage of starburst galaxies in terms of star formation history. Although the samples of high-redshift galaxies are still too small for statistical studies, the preliminary results give insight into the nature and evolution of distant star-forming objects and their link with present-day galaxies.

Physical properties of two low-luminosity $\mathsf{{\vec z} \sim 1.9}$ galaxies behind the lensing cluster AC 114

We present VLT/ISAAC near-infrared spectroscopy of two gravitationally-lensed z ~ 1.9 galaxies, A2 and S2, located behind the cluster AC 114. Thanks to large magnification factors, we have been successful in detecting rest-frame optical emission lines in star-forming galaxies 1 to 2 magnitudes fainter than in previous studies of Lyman break galaxies (LBGs) at z ~ 3. From the Ha luminosity, we estimate star formation rates (SFRs) which are 7 to 15 times higher than those inferred from the UV continuum flux at 1500 ang without dust extinction correction. The behavior of S2 and A2 in terms of O/H and N/O abundance ratios are very different, and they are also different from typical LBGs at z ~ 3. S2 is a low-metallicity object (Z ~ 0.03 Zsun) with a low N/O ratio, similar to those derived in the most metal-poor nearby HII galaxies. In contrast, A2 is a high-metallicity galaxy (Z ~ 1.3 Zsun) with a high N/O abundance ratio, similar to those derived in the most metal-rich starburst nucleus galaxies. The virial masses, derived from emission-line widths, are 0.5 and 2.4 x 10^10 Msun, for S2 and A2 respectively. Thanks to the gravitational amplification, the line profiles of S2 are spatially resolved, leading to a velocity gradient of +- 240 km/s, which yields a dynamical mass of ~ 1.3 x 10^10 Msun within the inner 1 kpc radius. Combining these new data with the sample of LBGs at z ~ 3, we conclude that these three galaxies exhibit different physical properties in terms of SFRs, abundance and mass-to-light ratios, and reddening. High-redshift galaxies of different luminosities could thus have quite different star formation histories (abridged version).

Resolved shocks in clumpy media

We study the structure of shocks in clumpy media, using a multifluid formalism. As expected, shocks broaden as they weaken: for sufficiently weak shocks, no viscous subshock appears in the structure. This has significant implications for the survival of dense clouds in regions overrun by shocks in a wide range of astrophysical circumstances, from planetary nebulae to the nuclei of starburst galaxies.

Near-infrared spectroscopy of starburst galaxies

We present new K-band spectroscopy for a sample of 48 starburst galaxies, obtained using UKIRT in Hawaii. This constitutes a fair sample of the most common types of starburst galaxies found in the nearby Universe, containing galaxies with different morphologies, masses and metallicities, with far-infrared luminosity LIR<1010 L⊙. The variety of near-infrared spectral features shown by these galaxies implies different bursts characteristics, which suggests that we survey galaxies with different star formation histories or at different stages of their burst evolution. Using synthetic starburst models, we conclude that the ensemble of parameters that best describes starburst galaxies in the nearby Universe is a constant rate of star formation, a Salpeter initial mass function (IMF) with an upper mass cut-off of Mup=30 M⊙ and bursts ages between 10 Myr and 1 Gyr. The model is fully consistent with the differences observed in the optical and far-infrared (FIR) between the different types of starbursts. It suggests that H ii galaxies have younger bursts and lower metallicities than starburst nucleus galaxies (SBNGs), while luminous infrared galaxies (LIRGs) have younger bursts but higher metallicities. Although the above solution from the synthetic starburst model is fully consistent with our data, it may not constitute a strong constraint on the duration of the bursts and the IMF. A possible alternative may be a sequence of short bursts (which may follow an universal IMF) over a relatively long period of time. In favour of the multiple-burst hypothesis, we distinguish in our spectra some variations of near-infrared (NIR) features with the aperture that can be interpreted as evidence that the burst regions are not homogeneous in space and time. We also found that the burst stellar populations are dominated by early-type B stars, a characteristic which seems difficult to explain with only one evolved burst. Our observations suggest that the starburst phenomenon must be a sustained or self-sustained phenomenon: either star formation is continuous in time, or multiple bursts happen in sequence over a relatively long period of time. The generality of our observations implies that this is a characteristic of starburst galaxies in the nearby Universe.

The Role of Starbursts in the Evolution of Galaxies

We have determined, for the first time, the nitrogen-to-oxygen abundance ratio (N/O) for a large sample of starburst nucleus galaxies (SBNGs) and compared it to the values observed in normal spiral galaxies. The N/O ratios in SBNGs are ∼ 0.2 dex higher than in normal HII regions observed in the discs of late-type spirals, but are comparable to the values found in the bulges of normal early-type spirals. The variation of the N/O ratio as a function of metallicity follows a primary + secondary relation, but the increase in nitrogen does not appear as a continuous process. Assuming that nitrogen is produced by intermediate-mass stars, we show that our observations are consistent with a model in which the bulk of the nitrogen was formed during past sequences of bursts of star formation which have probably started 2 or 3 Gyr in the past. What we observe, therefore, could be the main production of nitrogen in the bulges of these galaxies.

Surface photometry of emission-line galaxies in low density regions

Detailed B and R surface photometry is performed for 139 faint emission-line galaxies (ELGs) and for 2 non-ELGs. They are a subsample of the ELG sample selected by Popescu et al. (1996, 1998) towards four nearby voids. We derived the isophotal and integral photometric parameters and radial surface brightness (SB) profiles. Our sample consists mostly of low luminosity (), small linear size ( = 6.0 kpc) ( H 0 = 75 km s -1 Mpc -1 ) and blue ( = 0.93) galaxies. About 83% of the studied ELGs belong to the class of Blue Compact Galaxies (BCGs); others are luminous Starburst Nucleus Galaxies (SBNs) and a few interacting pairs. 72% of the ELGs possess a single dominant HII region, while the remaining 28% show multiple knots. Furthermore 71% of the ELGs show regular outer isophotes, and the remaining 29% reveal disturbed outer morphologies. We performed the SB profile decomposition by means of disentangling the underlying stellar disk and the excess light above the exponential disk. We classified the profiles into 5 types: pure disk profiles (21% of studied 139 ELGs); profiles that show both disk and bulge/nucleus/HII knot components (37%); profiles that have central light depression (13%); non-disky (concave) profiles (7%); and almost unresolved (quasi-stellar) images and stellar SB profiles (22%). Popescu et al. ((1997) found that most of the studied ELGs follow the spatial distribution of “normal” galaxies from the CfA Redshift Survey. 15 ELGs and 1 non-ELG were classified as being well isolated and are distributed within nearby ( 0.033) voids. We found that these isolated ELGs are almost all dwarf galaxies with , they show similar luminosities and colours as the nearby non-isolated ELGs. For 8 of 15 isolated ELGs an underlying LSBG has been detected. The underlying disks of isolated ELGs tend to be larger and of lower SB, than the disks of non-isolated ELGs (of the same total blue flux).

Optical Long‐Slit Spectroscopy of a Sample of Spiral Galaxies

ABSTRACTWe have analyzed long‐slit spectra of a sample of 11 spiral galaxies. We identify several disk H ii regions in each galaxy and provide classifications for the nuclear spectra. We find seven nuclear H ii region galaxies, including four starburst nucleus galaxies, and four LINERs.

Optical Classification of Megamaser Galaxies

We have obtained spectroscopic observations of the nuclear regions of 42 galaxies known to harbor strong OH masers. These megamaser galaxies represent a subsample of FIR (ultra)luminous galaxies, which typically have FIR luminosities in excess of 1011 L☉. The primary goal of this study is to investigate the nuclear activity sources of OH megamaser galaxies. We are able to classify the nuclear emission-line of all but one of our sample, and we find that this class of galaxies is dominated by active galactic nuclei (AGNs), although starburst galaxies do make up an appreciable fraction of the megamasers as well. Fully 45% of the megamasers exhibit Seyfert or LINER spectra, predominantly of Seyfert 2 type, although two galaxies with broad lines are observed. This observation is consistent with the current unification models for the two types of Seyfert activity, since the assumed geometry necessary to detect a megamaser places the Seyfert nucleus behind a high column density of molecular gas (i.e., the molecular torus). Starburst-nucleus galaxies comprise 32.5% of our sample, while 22.5% are classified as composite nuclear spectra (CSN) sources, showing evidence of both AGN and starburst activity. A number of objects show unusual emission-line ratios, not surprising for a group of galaxies that are known a priori to possess substantial absorbing material along the line of sight to their nuclei. Our results are compared to previous studies of FIR-selected galaxy samples, as well as to radio-continuum observations of these galaxies. The activity classification obtained from the radio data disagrees with the optical classifications in roughly 25% of the sources; we discuss possible explanations for these discrepancies.

The Pico dos Dias Survey Starburst Galaxies

We discuss the nature of the galaxies found in the Pico dos Dias Survey (PDS) for young stellar objects. The PDS galaxies were selected from the IRAS Point Source catalog. They have flux density of moderate or high quality at 12, 25, and 60 μm and spectral indices in the ranges -3.00 ≤ α(25, 12) ≤ + 0.35 and -2.50 ≤ α(60, 25) ≤ +0.85. These criteria allowed the detection of 382 galaxies, which are a mixture of starburst and Seyfert galaxies. Most of the PDS Seyfert galaxies are included in the catalog of warm IRAS sources by de Grijp et al. The remaining galaxies constitute a homogeneous sample of luminous [log F (LB/L☉) = 9.9 ± 0.4] starburst galaxies, 67% of which were not recognized as such before. The starburst nature of the PDS galaxies is established by comparing their LIR/LB ratios and IRAS colors with a sample of emission-line galaxies from the literature already classified as starburst galaxies. The starburst galaxies show an excess of FIR luminosity, and their IRAS colors are significantly different from those of Seyfert galaxies-99% of the starburst galaxies in our sample have a spectral index α(60, 25) -2.5. This color cutoff also marks a change in the dominant morphologies of the galaxies: the normal IRAS galaxies are preferentially late-type spirals (Sb and later), while the starbursts are more numerous among early-type spirals (earlier than Sbc). This preference of starbursts for early-type spirals is not new, but a trait of the massive starburst nucleus galaxies (Coziol et al.). As in other starburst nucleus galaxy samples, the PDS starbursts show no preference for barred galaxies. No difference is found between the starbursts detected in the FIR and those detected on the basis of UV excess. The PDS starburst galaxies represent the FIR luminous branch of the UV-bright starburst nucleus galaxies, with mean FIR luminosity log (LIR/L☉) = 10.3 ± 0.5 and redshifts smaller than 0.1. They form a complete sample limited in flux in the FIR at 2 × 10-10 ergs cm-2 s-1.

Starbursts in barred spiral galaxies

This paper presents optical long-slit spectroscopic observations of 105 barred Markarian IRAS galaxies. These observations are used to determine the spectral type (starburst or Seyfert) of emission-line regions in the nucleus and along the bar of the galaxies, in order to define a homogeneous sample of Starburst Nucleus Galaxies (SBNGs). Our selection criteria (ultraviolet excess, far infrared emission and barred morphology) have been very efficient for selecting star-forming galaxies, since our sample of 221 emission-line regions includes 82% nuclear or extranuclear starbursts. The contamination by Seyferts is low (9%). The remaining galaxies (9%) are objects with ambiguous classification (Hii or LINER). The dust content and Hα luminosity increase towards the nuclei of the galaxies. No significant variation of the electron density is found between nuclear and bar Hii regions. However, the mean Hα luminosity and electron density in the bar are higher than in typical disk Hii regions. We investigate different mechanisms for explaining the excess of nitrogen emission observed in our starburst nuclei. There is no evidence for the presence of a weak hidden active galactic nucleus in our starburst galaxies. The cause of this excess is probably a selective enrichment of nitrogen in the nuclei of the galaxies, following a succession of short and intense bursts of star formation. Our sample of SBNGs, located at a mean redshift of ~0.015, has moderate Hα ( erg s-1) and far infrared ( ) luminosities. The types are distributed equally among early- and late-type giant spirals with a slight preference for Sbc/Sc types because of their barred morphology. The majority (62%) of SBNGs are isolated with no sign of gravitational interaction. In terms of distance, luminosity and level of interaction, SBNGs are intermediate between Hii galaxies and luminous infrared galaxies.

The Evolution of Galaxies in Compact Groups

We present an analysis of the spectra of 62 galaxies in 15 compact groups. The galaxies are classified into four activity classes: galaxies without emission, starburst galaxies, luminous AGNs (Seyfert and LINERs), and low-luminosity AGNs (LLAGNs). The star formation in the Hickson compact group (HCG) starbursts is more intense than in normal spirals, but comparable to that observed in starburst-nucleus galaxies (SBNGs) in the field. In general, the HCG starbursts have mean solar gas metallicity and do not follow the metallicity-luminosity relation traced by the early-type SBNGs in the field, suggesting that most of them are late-type SBNGs. This morphology preference, coupled with the observation that the HCG starbursts are predominantly located in the halos of the groups, is consistent with the idea that compact groups are embedded in sparser structures. The stellar metallicities of the nonstarburst galaxies are comparable to those observed in normal galaxies with similar morphologies, but are relatively high for their luminosities. In these galaxies, the metal absorption line equivalent widths are slightly narrower than normal, while the Balmer absorption lines are relatively strong. All these observations suggest the presence of a population of intermediate-age stars. These galaxies could be poststarburst, but at a very advanced stage of evolution, the last bursts having happened more than 2 Gyr in the past. Our observations support a scenario in which the cores of the groups are slowly collapsing evolved systems embedded in more extended structures. In the cores of the groups, the interactions were more frequent and the galaxies evolved at a more rapid rate than in their halos.

The Chemical Evolution of Starburst Nucleus Galaxies

The metallicities derived from spectroscopic observations of a sample of Starburst Nucleus Galaxies (SBNGs) are compared to those of several other types of galaxies (normal giant galaxies, Irregular and HII galaxies) drawn from the literature. The SBNGs are deficient in metals with respect to normal galaxies of same morphological type, suggesting that - SBNGs are galaxies still in the process of formation. Breaking the SBNGs into early-types (Sb and earlier) and late-types reveals that the former seem to follow the same linear luminosity-metallicity relation as the irregular and elliptical galaxies, whereas the latter and the giant spirals show comparable (0.2 and 0.3 dex) excess abundances with respect to the linear relation. This difference between the two types of SBNGs is consistent with the predictions of the model of hierarchical formation of galaxies: the early-type SBNGs are building their bulges by successive mergers of small stellar and gaseous systems, while the late-type SBNGs are mostly accreting gas to form a disk.

The Montreal Blue Galaxy Survey.III.Third List of UV-Bright Candidates

We present and discuss the latest addition of the Montreal Blue Galaxy (MBG) survey. Inspection of 59 Curtis Schmidt plates resulted in the identification of 135 new UV-bright galaxies with B < 15.5. This brings the total number of MBGs to 469. New results of the $V/V_m$ test show that our survey is complete to B = 14.7. From our most recent spectroscopic follow-up, we confirm the discovery of one new Seyfert 1 galaxy and possibly one new Seyfert 2 galaxy. We confirm also the bias of the MBG survey towards the low-excitation and metal rich Starburst Nucleus Galaxies (SBNGs). The spectral characteristics of the MBGs are similar to those of the infrared luminous IRAS galaxies. As a common characteristic, they show a mean ratio Log([NII]/H$\alpha$) in excess of 0.2 dex as compared to normal disk HII regions. In general, the MBGs have lower far-infrared luminosities ($L_{IR} < 10^{11} L_{\odot}$) and are nearer (z < 0.05) than the luminous IRAS galaxies. The distribution of the morphologies of the MBGs indicates a high number of early-type spirals (Sb and earlier). Nearly half of these galaxies also possess a bar. In our sample, the fraction of galaxies with bars depends on the morphology and increases towards the late-type spirals. However, if we consider only isolated galaxies, the late-type spirals show a clear tendency to be barred. Signs of a recent interaction with neighbor galaxies are obvious only in 24% of our candidates. Although this number is only a lower limit, it is nevertheless sufficiently low to suggest that in a majority of massive galaxies the burst of star formation do not depends solely on dynamical processes.

The Montreal Blue Galaxy survey. 2: Second list of UV-bright candidates

view Abstract Citations (36) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Montreal Blue Galaxy Survey. II. Second List of UV-Bright Candidates Coziol, Roger ; Demers, Serge ; Pena, Miriam ; Barneoud, Remi Abstract We present and discuss the second list of the Montreal Blue Galaxy survey. Following the inspection of 71 plates, we found 237 new candidates with B < 15.5. 73 percent of them are also detected by IRAS. Spectrophotometry was carried out, at medium resolution, for a subset of 40 objects leading to the identification of three new AGNs and producing 13 new radial velocities. Spectral classification of our candidates confirms our previous finding !hat the majority of our candidates are starburst nucleus galaxies similar to the objects studied by Balzano [ApJ, 268, 602(1983)]. Our survey is biased against the high excitation starburst H II galaxies and the LINER galaxies. Metallicities of our galaxies are found to be from log (O/H) = 8.4 to 9.0, which suggests galaxies in advanced stages of chemical evolution. Publication: The Astronomical Journal Pub Date: August 1994 DOI: 10.1086/117079 Bibcode: 1994AJ....108..405C Keywords: Active Galactic Nuclei; H Ii Regions; Sky Surveys (Astronomy); Starburst Galaxies; Ultraviolet Emission; Emission Spectra; Infrared Astronomy Satellite; Red Shift; Spectral Line Width; Stellar Spectrophotometry; Tables (Data); Astronomy; SURVEYS; GALAXIES: STARBURST; GALAXIES: ACTIVE full text sources ADS | data products NED (245) SIMBAD (235) CDS (1) Related Materials (2) Part 1: 1993AJ....105...35C Part 3: 1997AJ....113.1548C

The Starburst in the Nucleus of NGC 6764: The Near-IR/Radio/Optical Connection

Knowledge of the distribution and excitation of gas close to the nuclei of starburst galaxies is an essential element in the construction of models dealing with intense, but short-lived, star forming events. Building a comprehensive picture of the concentrations of various gaseous components in such regions calls for a multi-wavelength approach: the principal cooling lines of cold (T≤200K) molecular gas fall in the millimetre waveband, those of hot (T~1−3×103K) excited molecular material in the near-IR, and those pinpointing starburst activity in the optical. In many cases the extents of the emitting regions are on the order of only a few arcseconds.As part of such a study into the relationship between various near- and circum- nuclear gaseous components in starburst galaxies, we have obtained data on NGC 6764, a barred spiral classified as a LINER, at resolutions of 1″−4″ across the optical, near-infrared and millimetre wavelength regimes. In a previous paper (Eckart et al. 1991) we discussed extensive single dish millimetre and JHK near-IR measurements of the nucleus and disk of NGC 6764. Here we present new near-IR observations obtained with the MPE FAST instrument (Rotaciuc et al. 1991) at the William Herschel Telescope, along with 2″ resolution 12CO J=1-0 (115 GHz) interferometry measured with the Nobeyama millimeter array and 1″ optical spectroscopy from the 3.5m Calar Alto telescope.