We investigate the size--density relation in extragalactic HII regions, with the aim of understanding the role of dust and different physical conditions in the ionized medium. First, we compiled several observational data sets for Galactic and extragalactic HII regions and confirm that extragalactic HII regions follow the same size (D)--density (n) relation as Galactic ones. Motivated by the inability of static models to explain this, we then modelled the evolution of the size--density relation of HII regions by considering their star formation history, the effects of dust, and pressure-driven expansion. The results are compared with our sample data whose size and density span roughly six orders of magnitude. We find that the extragalactic size--density relation does not result from an evolutionary sequence of HII regions but rather reflects a sequence with different initial gas densities (``density hierarchy''). Moreover, the size of many HII regions is limited by dust absorption of ionizing photons, rather than consumption by ionizing neutral hydrogen. Dust extinction of ionizing photons is particularly severe over the entire lifetime of compact HII regions with typical gas densities of greater than 10^3 cm^{-3}. Hence, as long as the number of ionizing photons is used to trace massive star formation, much star-formation activity could be missed. Such compact dense environments, the ones most profoundly obscured by dust, have properties similar to ``maximum--intensity starbursts''. This implies that submillimeter and infrared wavelengths may be necessary to accurately assess star formation in these extreme conditions both locally and at high redshift.
We present a review on the determination of the primordial helium abundance Yp, based on the study of hydrogen and helium recombination lines in extragalactic HII regions. We also discuss the observational determinations of the increase of helium to the increase of oxygen by mass Delta Y / Delta O, and compare them with predictions based on models of galactic chemical evolution.
We report the first results of a long term program aiming to provide accurate independent estimates of the Hubble constant (H0) using the L-sigma distance estimator for Giant extragalactic HII regions (GEHR) and HII galaxies. We have used VLT and Subaru high dispersion spectroscopic observations of a local sample of HII galaxies, identified in the SDSS DR7 catalogue in order to re-define and improve the L(Hbeta)-sigma distance indicator and to determine the Hubble constant. To this end we utilized as local calibration or `anchor' of this correlation, GEHR in nearby galaxies which have accurate…
Cosmological applications of HII galaxies (HIIGx) and giant extragalactic HII regions (GEHR) to construct the Hubble diagram at higher redshifts require knowledge of the "$L$--$σ$" relation of the standard candles used. In this paper, we study the properties of a large sample of 156 sources (25 high-$z$ HII galaxies, 107 local HII galaxies, and 24 giant extragalactic HII regions) compiled by Terlevich et al.(2015). Using the the cosmological distances reconstructed through two new cosmology-independent methods, we investigate the correlation between the H$β$ emission-line luminosity $L$ and io…
We present very deep spectrophotometry of 14 bright extragalactic HII regions belonging to spiral, irregular, and blue compact galaxies. The data for 13 objects were taken with the HIRES echelle spectrograph on the Keck I telescope. We have measured CII recombination lines in 10 of the objects and OII recombination lines in 8 of them. We have determined electron temperatures from line ratios of several ions, specially of low ionization potential ones. We have found a rather tight linear empirical relation between Te([NII]) and Te([OIII]). We have found that OII lines give always larger abundan…
In an attempt to remove the systematic errors which have plagued the calibration of the HII region abundance sequence, we have theoretically modeled the extragalactic HII region sequence. We then used the theoretical spectra so generated in a double blind experiment to recover the chemical abundances using both the classical electron temperature + ionization correction factor technique, and the technique which depends on the use of strong emission lines (SELs) in the nebular spectrum to estimate the abundance of oxygen. We find a number of systematic trends, and we provide correction formulae …
Spectra of high-metallicity (12+log(O/H) > 8.2) HII regions where oxygen auroral lines are measurable in both the O+ and O++ zones, have been extracted from the Data Release 6 of the Sloan Digital Sky Survey (SDSS). Our final sample consists of 181 SDSS spectra of HII regions in galaxies in the redshift range from ~0.025 to ~0.17. The t_2,O-t_3,O diagram is examined. In the SDSS HII regions, the electron temperature t_2,O is found to have a large scatter at a given value of the electron temperature t_3,O. The majority of the SDSS HII regions lie below the t_2,O-t_3,O relation derived for HII r…
(Abridged) We have obtained new spectrophotometric data for 28 HII regions in the spiral galaxy NGC 300, a member of the nearby Sculptor Group. The detection of auroral lines, including [OIII]4363, [SIII]6312 and [NII]5755, has allowed us to measure electron temperatures and direct chemical abundances for the whole sample. We determine for the first time in this galaxy a radial gas-phase oxygen abundance gradient based solely on auroral lines, and obtain the following least-square solution: 12+log(O/H)=8.57-0.41 R/R25, where the galactocentric distance is expressed in terms of the isophotal ra…
We present long slit spectrophotometry considering the presence of thermal inhomogeneities (t^2) of two HII regions in the Small Magellanic Cloud (SMC): NGC 456 and NGC 460. Physical conditions and chemical abundances were determined for three positions in NGC 456 and one position in NGC 460, first under the assumption of uniform temperature and then allowing for the possibility of thermal inhomogeneities. We determined t^2 values based on three different methods: i) by comparing the temperature derived using oxygen forbidden lines with the temperature derived using helium recombination lines,…
The abundance of polycyclic aromatic hydrocarbons (PAHs) in low- and high-metallicity galaxies has been widely discussed since the time when detailed infrared data for extragalactic objects were first obtained. On the scales of entire galaxies, a smaller PAH abundance in lower-metallicity galaxies is often observed. We study this relationship for star-forming regions in nearby galaxies, for a sample containing more than 200 HII complexes, using spatially-resolved observations from the Herschel Space Observatory and Spitzer Space Telescope. We use a model for the dust emission to estimate the p…
We present a study of the kinematic properties of the ionized gas in the dominant giant HII region of the well known HII galaxy: II Zw 40. High spatial and spectral resolution spectroscopy has been obtained using IFU mode on the GMOS instrument at Gemini-North telescope. We have used a set of kinematics diagnostic diagrams, such as the intensity vs. velocity dispersion intensity vs. radial velocity, for global and individual analysis in sub-regions of the nebula. We aim to separate the main line broadening mechanisms responsible for producing a smooth supersonic integrated line profile for the…
The electron temperatures of high-metallicity (12+log(O/H) > 8.2) HII regions have been studied. The empirical ff relations which express the nebular-to- auroral [OIII] line ratio Q_3,O (as well as the nebular-to-auroral [OII] line ratio Q_2,O, and the nebular-to-auroral [NII] line ratio Q_2,N) in terms of the nebular R_3 and R_2 line fluxes in spectra of high-metallicity HII regions are derived, and the electron temperatures t_3,O, t_2,O, and t_2,N in a number of extragalactic HII regions are also determined. Furthermore, the t_2 - t_3 diagram is discussed. It is found that there is a one-to-…
We present for the first time a new data set of emission line widths for 118 star-forming regions in HII galaxies (HIIGs). This homogeneous set is used to investigate the L-sigma relation in conjunction with optical spectrophotometric observations. Peculiarities in the line profiles such as sharp lines, wings, asymmetries, and in some cases more than one component in emission were verified. From a new independent homogeneous set of spectrophotometric data we derived physical condition parameters and performed the statistical principal component analysis. We have investigated the potential role…
The Hubble diagram constructed using HII galaxies (HIIGx) and Giant extragalactic HII regions (GEHR) as standard candles already extends beyond the current reach of Type Ia SNe. A sample of 156 HIIGx and GEHR sources has been used previously to compare the predictions of LCDM and R_h=ct, the results of which suggested that the HIIGx and GEHR sources strongly favour the latter over the former. But this analysis was based on the application of parametric fits to the data and the use of information criteria, which disfavour the less parsimonious models. In this paper, we advance the use of HII so…
We present chemical evolution models of the Galactic disk with different Z-dependent yields. We find that a moderate mass loss rate for massive stars of solar metallicity produces an excellent fit to the observed C/H and C/O gradients of the Galactic disk. The best model also fits: the H, He, C, and O abundances derived from recombination lines of M17, the protosolar abundances,and the C/O-O/H, C/Fe-Fe/H, and O/Fe-Fe/H relations derived from solar vicinity stars. The agreement of the model with the protosolar abundances implies that the Sun originated at a galactocentric distance similar to th…
The HII complex N159 in the Large Magellanic Cloud (LMC) is used to study massive star formation in different environments, as it contains three giant molecular clouds (GMCs) that have similar sizes and masses but exhibit different intensities of star formation. We identify candidate massive young stellar objects (YSOs) using infrared photometry, and model their SEDs to constrain mass and evolutionary state. Good fits are obtained for less evolved Type I, I/II, and II sources. Our analysis suggests that there are massive embedded YSOs in N159B, a maser source, and several ultracompact HII regi…
Using deep Subaru/FOCAS spectra of 34 HII regions in both the inner and outer parts of the extended ultraviolet (XUV) disc galaxy NGC 4625 we have measured an abundance gradient out to almost 2.5 times the optical isophotal radius. We applied several strong line abundance calibrations to determine the HII region abundances, including R23, [NII]/[OII], [NII]/Ha as well as the [OIII]4363 auroral line, which we detected in three of the HII regions. We find that at the transition between the inner and outer disc the abundance gradient becomes flatter. In addition, there appears to be an abundance …
The correlation between emission-line luminosity (L) and profile width (sigma) for HII Galaxies provides a powerful method to measure the distances to galaxies over a wide range of redshifts. In this paper we use SDSS spectrophotometry to explore the systematics of the correlation using the [OIII]5007 lines instead of Halpha or Hbeta to measure luminosities and line widths. We also examine possible systematic effects involved in measuring the profile-widths and the luminosities through different apertures. We find that the green L-sigma relation defined using [OIII]5007 luminosities is signifi…
(abridged)The focus of this work is to study mid-infrared point sources and the diffuse interstellar medium (ISM) in the low-metallicity (~0.2 solar) giant HII region N66 using the Spitzer Space Telescope's Infrared Spectrograph. We study 14 targeted infrared point sources as well as spectra of the diffuse ISM that is representative of both the photodissociation regions (PDRs) and the HII regions. Among the point source spectra, we spectroscopically confirm that the brightest mid-infrared point source is a massive embedded young stellar object, we detect silicates in emission associated with t…
We investigate the relation between star formation rate (SFR) and gas surface densities in Galactic star forming regions using a sample of YSOs and massive clumps. Our YSO sample consists of objects located in 20 molecular clouds from the Spitzer cores to disks and Gould's Belt surveys. We estimate the gas surface density (Sigma_gas) from Av maps and YSO SFR surface densities (Sigma_SFR) from the number of YSOs, assuming a mean mass and lifetime. We also divide the clouds into contour levels of Av, counting only the youngest Class I and Flat SED YSOs. For a sample of massive star forming clump…
We demonstrate the existence of a -local- relation between galaxy surface mass density, gas metallicity, and star-formation rate density using spatially-resolved optical spectroscopy of HII regions in the local Universe. One of the projections of this distribution, -the local mass-metallicity relation- extends over three orders of magnitude in galaxy mass density and a factor of eight in gas metallicity. We explain the new relation as the combined effect of the differential radial distributions of mass and metallicity in the discs of galaxies, and a selective star-formation efficiency. We use …
The relationship between the integrated H$β$ line luminosity and the velocity dispersion of the ionized gas of HII galaxies and giant HII regions represents an exciting standard candle that presently can be used up to redshifts z ~ 4. Locally it is used to obtain precise measurements of the Hubble constant by combining the slope of the relation obtained from nearby ($z \leq $ 0.2) HII galaxies with the zero point determined from giant HII regions belonging to an `anchor sample' of galaxies for which accurate redshift-independent distance moduli are available. We present new data for 36 giant H…
Redshift Evolution of the HII Galaxy $L$-$σ$ Relation: Gaussian Process Analysis and Cosmological Implications
Institute of Theoretical Physics, School of Physics, Dalian University of Technology（大连理工大学物理学院理论物理研究所）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；College of Astronomy and Space Sciences, University of Chinese Academy of Sciences（中国科学院大学天文学与空间科学学院）
The Baryonic Mass-Halo Mass Relation of Extragalactic Systems
Case Western Reserve University（凯斯西储大学）；Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理研究所）；Università degli Studi di Firenze（佛罗伦萨大学）；INAF — Arcetri Astrophysical Observatory（意大利国家天体物理研究所——阿切特里天文台）；University of Oregon（俄勒冈大学）；Nanjing University（南京大学）
We have computed a series of realistic and self-consistent models that have been shown to be able to reproduce the emitted spectra of HII galaxies in a star bursting scenario (Martin-Majon et al. 2008). Our models combine different codes of chemical evolution, evolutionary population synthesis and photoionization. The emitted spectrum of HII galaxies is reproduced by means of the photoionization code CLOUDY (Ferland, 1998), using as ionizing spectrum the spectral energy distribution (SED) of the modelled HII galaxy, calculated using the new and updated stellar population models PopStar (Molla …
Optical spectra of 25 H II regions in the inner two kpc of the M33 disk have been obtained with the GMOS spectrograph at the Gemini North telescope. The oxygen abundance gradient measured from the detection of the [O III]4363 auroral line displays a scatter of approximately 0.06 dex, a much smaller value than recently reported by Rosolowsky & Simon in this galaxy. The analysis of the abundances for a large sample of H II regions derived from the R23 strong-line indicator confirms that the scatter is small over the full disk of M33, consistent with the measuring uncertainties, and comparable to…
In this paper we investigate scaling relations between star formation rates and molecular gas masses for both local Galactic clouds and a sample of external galaxies. We specifically consider relations between the star formation rates and measurements of dense, as well as total, molecular gas masses. We argue that there is a fundamental empirical scaling relation that directly connects the local star formation process with that operating globally within galaxies. Specifically, the total star formation rate in a molecular cloud or galaxy is linearly proportional to the mass of dense gas within …
We present HST/WFC3 narrow-band imaging of the starburst galaxy M83 targeting the hydrogen recombination lines (H$β$, H$α$ and Pa$β$), which we use to investigate the dust extinction in the HII regions. We derive extinction maps with 6 parsec spatial resolution from two combinations of hydrogen lines (H$α$/H$β$ and H$α$/Pa$β$), and show that the longer wavelengths probe larger optical depths, with $A_V$ values larger by $\gtrsim$1 mag than those derived from the shorter wavelengths. This difference leads to a factor $\gtrsim$2 discrepancy in the extinction-corrected H$α$ luminosity, a signific…
The $L-σ$ relation of HII galaxies (HIIGx) calibrated by a distance indicator is a reliable standard candle for measuring the Hubble constant $H_0$. The most straightforward calibration technique anchors them with the first tier of distance ladders from the same galaxies. Recently another promising method that uses the cosmological model-independent Cosmic Chronometers (CC) as a calibrator has been proposed. We promote this technique by removing the assumptions about the cosmic flatness and using a non-parametric Artificial Neural Network for the data reconstruction process. We observe a corre…
We outline to the community the value of a Magellanic Clouds Survey that consists of three components: I) a complete-area, high resolution, multi-band UV-near-IR broadband survey; II) a narrowband survey in 7 key nebular filters to cover a statistically significant sample of representative HII regions and a large-area, contiguous survey of the diffuse, warm ISM; and III) a comprehensive FUV spectroscopic survey of 1300 early-type stars. The science areas enabled by such a dataset are as follows: A) assessment of massive star feedback in both HII regions and the diffuse, warm ISM; B) completion…
We present the integrated Halpha emission line profile for 157 HII regions in the central 3.4' x 3.4' of the galaxy M 83 (NGC 5236). Using the Fabry-Perot interferometer GHaFaS, on the 4.2 m William Herschel on La Palma, we show the importance of a good characterization of the instrumental response function for the study of line profile shapes. The luminosity-velocity dispersion relation is also studied, and in the log(L)-log(sigma) plane we do not find a linear relation, but an upper envelope with equation log(L)=0.9 *log(sigma)+38.1. For the adopted distance of 4.5 Mpc, the upper envelope ap…
Revisiting the cosmic distance duality relation with machine learning reconstruction methods: the combination of HII galaxies and ultra-compact radio quasars
Using the OSIRIS tunable narrow band imager on the 10.4m GTC (La Palma) we have mapped the SAB(rs)cd galaxy NGC 6946 over a 7.3x7.5 square arcminutes field in the emission lines of the [SII]λλ, 6717, 6731 doublet, and in Hα. From these maps we have produced catalogs of the Hαluminosities and effective radii of 557 HII regions across the disk, and derived the [SII] emission line ratios of 370 of these. The Hαobservations were used to derive the mean luminosity-weighted electron densities for the regions of the sample, while the [SII] line ratios allowed us to derive values of the in situ electr…
We propose to use HII galaxies (HIIG) to trace the redshift-distance relation, by means of their $L(\mathrm{H}β) - σ$ correlation, in an attempt to constrain the dark energy equation of state parameter solution space, as an alternative to the cosmological use of type Ia supernovae. For a sample of 128 local compact HIIG with high equivalent widths of their Balmer emission lines we obtained ionised gas velocity dispersion from high S/N, high-dispersion spectroscopy (Subaru-HDS and ESO VLT-UVES) and integrated H$β$ fluxes from low dispersion wide aperture spectrophotometry. We find that the $L(\…
We analyse the internal dynamics of star-forming HII regions and their efficiency in interacting with the ISM. We use GHaFaS (Fabry-Perot) data of the nearby spiral galaxy M83 to perform multiple-Gaussian fitting to the integrated Halpha emission line for 136 HII regions, advanced instrumental response subtraction and to study the Luminosity-velocity dispersion relation. We find that the best way of dealing with instrumental response effects is convolving its actual shape with the Gaussian before fitting and that in our data almost none of the regions need a secondary Gaussian.
We present the properties of 8 star-forming regions, or 'clumps,' in 3 galaxies at z~1.3 from the WiggleZ Dark Energy Survey, which are resolved with the OSIRIS integral field spectrograph. Within turbulent discs, σ~90 km/s, clumps are measured with average sizes of 1.5 kpc and average Jeans masses of 4.2 x 10^9 \Msolar, in total accounting for 20-30 per cent of the stellar mass of the discs. These findings lend observational support to models that predict larger clumps will form as a result of higher disc velocity dispersions driven-up by cosmological gas accretion. As a consequence of the ch…
The Cepheid period-luminosity relation is the primary distance indicator used in most determinations of the Hubble constant. The tip of the red giant branch (TRGB) is an alternative basis. Using the new ANU SkyMapper Telescope, we calibrate the Tully Fisher relation in the I band. We find that the TRGB and Cepheid distance scales are consistent.
(abridged) We present 8.2m VLT spectroscopic observations of 28 HII regions in 16 emission-line galaxies and 3.6m ESO telescope spectroscopic observations of 38 HII regions in 28 emission-line galaxies. These emission-line galaxies were selected mainly from the Data Release 6 (DR6) of the Sloan Digital Sky Survey (SDSS) as metal-deficient galaxy candidates. We collect photometric and high-quality spectroscopic data for a large uniform sample of star forming galaxies including new observations. Our aim is to study the luminosity-metallicity (L-Z) relation for nearby galaxies, especially at its …
We have used the images from the ACS on HST in Halpha, and in the neighboring continuum, to produce flux calibrated images of the large spiral galaxy M51, and the dwarf irregular NGC 4449. From these images we have derived the absolute luminosities in Halpha, the areas, and the positions with respect to the galactic centers as reference points, of over 2600 HII regions in M51 and over 270 HII regions in NGC 4449. Using this database we have derived luminosity (L)--volume (V) relations for the regions in the two galaxies, showing that within the error limits these obey the equation L ~ V^(2/3),…
Recent models show that TP-AGB stars should dominate the NIR spectra of populations 0.3 to 2 Gyr old, leaving unique signatures that can be used to detect young/intermediate stellar population in galaxies. However, no homogeneous database of star-forming galaxies is available in the NIR to fully explore these results. With this in mind, we study the NIR spectra of a sample of 23 HII and starburst galaxies, aimed at characterizing the most prominent spectral features and continuum shape in the 0.8-2.4 micron region of these objects. Spectral indices are derived for the relevant absorption lines…
We present a new determination of the primordial helium mass fraction Yp, based on 93 spectra of 86 low-metallicity extragalactic HII regions, and taking into account the latest developments concerning systematic effects. These include collisional and fluorescent enhancements of HeI recombination lines, underlying HeI stellar absorption lines, collisional and fluorescent excitation of hydrogen lines and temperature and ionization structure of the HII region. Using Monte Carlo methods to solve simultaneously for the above systematic effects, we find the best value to be Yp=0.2565+/-0.0010(stat.…
We explore the possibility of setting stringent constraints to the Dark Energy equation of state using alternative cosmic tracers like: (a) the Hubble relation using HII galaxies, which can be observed at much higher redshifts (z~3.5) than those currently traced by SNIa samples, and (b) the large-scale structure using the clustering of X-ray selected AGN,which have a redshift distribution peaking at z~1. We use extensive Monte-Carlo simulations to define the optimal strategy for the recovery of the dark-energy equation of state using the high redshift (z~2) Hubble relation, but accounting also…
We show that star formation in the giant HII region NGC 5471 has been ongoing during the past 100 Myr. Using HST/WFPC2 F547M and F675W, ground based JHKs, and GALEX FUV and NUV images, we have conducted a photometric study of the star formation history in the massive giant extragalactic HII region NGC 5471 in M101. We perform a photometric study of the colour-magnitude diagram (CMD) of the resolved stars, and an integrated analysis of the main individual star forming clusters and of NGC 5471 as a whole. The integrated UV-optical-nIR photometry for the whole region provides two different refere…
