We aim to derive the chemical behavior of a significant sample of PNe and HII regions in the irregular galaxy NGC 6822 The selected objects are distributed in different zones of the galaxy. Due to the faintness of PNe and HII regions in NGC 6822, to gather spectroscopic data with large telescopes is necessary. We obtained a well suited sample of spectra by employing VLT-FORS 2 and Gemini-GMOS spectrographs. Ionic and total abundances are calculated for the objects where electron temperatures can be determined through the detection of [OIII] λ4363 or/and [NII] λ5755 lines. A "simple" chemical evolution model has been developed and the observed data are used to compute a model for NGC 6822 in order to infer a preliminary chemical history in this galaxy. Confident determinations of He, O, N, Ne, S and Ar abundances were derived for a sample of 11 PNe and one HII region. We confirm that the present ISM is chemically homogeneous, at least in the central 2 kpc of the galaxy, showing a value 12+log O/H = 8.06$\pm$0.04. From the abundance pattern of PNe, we identified two populations: a group of young PNe with abundances similar to HII regions and a group of older objects with abundances a factor of two lower. A couple of extreme Type I PNe were found. No third dredge-up O enrichement was detected in PNe of this galaxy. The abundance determinations allow us to discuss the chemical behavior of the present and past ISM in NGC 6822. Our preliminary chemical evolution model predicts that an important gas-mass lost occurred during the first 5.3 Gyr, that no star higher than 40 M$_\odot$ was formed, and that 1% of all 3-15 M$_\odot$ stars became binary systems progenitors to SNIa.
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 …
Using ACS-HST images to yield continuum subtracted photometric maps in Hαof the Sbc galaxy M51 and the dwarf irregular galaxy NGC 4449, we produced extensive (over 2000 regions for M51, over 200 regions for NGC4449) catalogues of parameters of their HII regions: their Hαluminosities, equivalent radii and coordinates with respect to the galaxy centers. From these data we derived, for each region, its mean luminosity weighted electron density, <n_e>, determined from the Hαluminosity and the radius, R, of the region. Plotting these densities against the radii of the regions we find excellent fits…
We are carrying out a detailed 2D spectroscopic study of the central 210 pc X 130 pc of the blue compact dwarf (BCD) galaxy NGC5253. This contribution presents the ionization conditions and chemical abundance patterns for the different kinematic components of the ionized gas detected in our previous work. All the kinematic components present an excess in nitrogen abundance. In particular, the broad velocity component has larger excess than the narrow one by a factor of ~1.4+-0.4 which is consistent with a scenario for the Giant HII Region where the broad component of the emission lines traces …
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),…
Spectroscopic observations of 63 HII regions in six spiral galaxies (NGC 628, NGC 783, NGC 2336, NGC 6217, NGC 7331, and NGC 7678) were carried out with the 6-meter telescope (BTA) of Russian Special Astrophysical Observatory with the Spectral Camera attached to the focal reducer SCORPIO in the multislit mode with a dispersion of 2.1A/pixel and a spectral resolution of 10A. These observations were used to estimate the oxygen and nitrogen abundances and the electron temperatures in HII regions through the recent variant of the strong line method (NS calibration). The parameters of the radial di…
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,…
We present new results from our search for Giant H\,{\sc ii} Regions in galaxies visible from the southern hemisphere. In this work we study two galaxies: NGC\,7479 and NGC\,6070. Using high-resolution spectra, obtained with different instruments at Las Campanas Observatory, we are able to resolve the emission-line profile widths and determine the intrinsic velocity dispersion of the ionised gas. We detect profile widths corresponding to supersonic velocity dispersions in the six observed H\,{\sc ii} regions. We find that all of them show at least two distinct kinematical components: a relativ…
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 suggest a new way of the determining abundances and electron temperatures in HII regions from strong emission lines. Our approach is based on the standard assumption that HII regions with similar intensities of strong emission lines have similar physical properties and abundances. A "counterpart" for a studied HII region may be chosen among HII regions with well-measured abundances (reference HII regions) by comparison of carefully chosen combinations of strong line intensities. Then the abundances in the investigated HII region can be assumed to be the same as that in its counterpart. In o…
To place meaningful constraints on Big Bang Nucleosynthesis models, the primordial helium abundance determination is crucial. Low-metallicity HII regions have been used to estimate it since their statistical uncertainties are relatively small. We present a new determination of the primordial helium abundance, based on long slit spectra of the HII region NGC 346 in the small Magellanic cloud. We obtained spectra using three $409'' \times 0.51''$ slits divided in 97 subsets. They cover the range $λ\lambda3600-7400$ of the electromagnetic spectrum. We used PyNeb and standard reduction procedures …
We have obtained deep spectra of 26 planetary nebulae (PNe) and 9 compact HII regions in the nearby spiral galaxy NGC 300, and analyzed them together with those of the giant HII regions previously observed. We have determined the physical properties of all these objects and their He, N, O, Ne, S and Ar abundances in a consistent way. We find that, globally, compact HII regions have abundance ratios similar to those of giant HII regions, while PNe have systematically larger N/O ratios and similar Ne/O and Ar/O ratios. We demonstrate that the nitrogen enhancement in PNe cannot be only due to sec…
We have carried out a detailed modelling of the dust heating and emission in the nearby, starbursting dwarf galaxy NGC 4214. Due to its proximity and the great wealth of data from the UV to the millimeter range (from GALEX, HST, {\it Spitzer}, Herschel, Planck and IRAM) it is possible to separately model the emission from HII regions and their associated photodissociation regions (PDRs) and the emission from diffuse dust. Furthermore, most model parameters can be directly determined from the data leaving very few free parameters. We can fit both the emission from HII+PDR regions and the diffus…
Using the Tremaine-Weinberg method, we measure the speed of the HI bar seen in the disk of NGC 3741. NGC 3741 is an extremely gas rich galaxy with an {H\,{\sc i}} disk which extends to about 8.3 times its Holmberg radius. It is also highly dark matter-dominated. Our calculated value of the pattern speed $Ω_p$ is 17.1 $\pm$ 3.4 km $\textrm{s}^{-1}\textrm{kpc}^{-1}$. We also find the ratio of the co-rotation radius to the bar semi-major axis to be (1.6 $\pm$ 0.3), indicating a slow bar. This is consistent with bar models in which dynamical friction results in a slow bar in dark matter dominated …
In order to better understand the impact of the bar on the evolution of spiral galaxies, we measure the properties of giant HII regions and the bar in the SB(s)b galaxy NGC5430. We use two complementary data sets, both obtained at the Observatoire du Mont-Mégantic: a hyperspectral data cube from the imaging Fourier transform spectrograph SpIOMM, and high-resolution spectra across the bar from a long-slit spectrograph. We flux-calibrate SpIOMM spectra for the first time, and produce Hα and [NII]λ6584Å intensity maps from which we identify 51 giant HII regions in the spiral arms and bar. We eval…
HII regions in the arms of spiral galaxies are indicators of recent star-forming processes. They may have been caused by the passage of the density wave or simply created by other means near the arms. The study of these regions may give us clues to clarifying the controversy over the existence of a triggering scenario, as proposed in the density wave theory. Using H$α$ direct imaging, we characterize the HII regions from a sample of three grand design galaxies: NGC5457, NGC628 and NGC6946. Broad band images in R and I were used to determine the position of the arms. The HII regions found to be…
Integral Field Spectroscopy obtained with PPak and the 3.5m telescope at the Calar Alto Observatory has been used to study an outer HII region complex in the well studied galaxy NGC 6946. This technique provides detailed maps of the region in different emission lines yielding spatially resolved information about the physical properties of the gas. The configuration was chosen to cover the whole spectrum from 3600 up to 10000 A. We selected four luminous knots, to perform a detailed integrated spectroscopic analysis of these structures and of the whole PPak field-of-view (FOV). For all the knot…
We present 13CO(J=1-0) line emission observations with the Nobeyama 45-m telescope toward the giant HII region NGC 604 in the spiral galaxy M 33. We detected 13CO(J=1-0) line emission in 3 major giant molecular clouds (GMCs) labeled as GMC-A, B, and C beginning at the north. We derived two line intensity ratios, 13CO(J=1-0)/12CO(J =1-0), R13/12, and 12CO(J=3-2)/12CO(J =1-0), R31, for each GMC at an angular resolution of 25" (100 pc). Averaged values of R13/12 and R31 are 0.06 and 0.31 within the whole GMC-A, 0.11 and 0.67 within the whole GMC-B, and 0.05 and 0.36 within the whole GMC-C, respec…
ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburst galaxies. We present for the first time in a starburst galaxy a 2D study of the spatial behavior of collisional and radiative transfer effects in He^+. The HeI lines are analysed based on data obtained with FLAMES and GMOS. Collisional effects are negligible for transitions in the singlet cascade while relatively important for those in the triplet cascade. In particular, they can contribute up to 20% of the flux in the HeIl7065 line. Radiative transfer effects are important over an extended and circular area of 30pc in …
We present a set of photoionization models that reproduce simultaneously the observed optical and mid-infrared spatial distribution of the HII region NGC595 in the disk of M33 using the code CLOUDY. Both optical (PMAS-Integral Field Spectroscopy) and mid-infrared (8 mi and 24 mi bands from Spitzer) data provide enough spatial resolution to model in a novel approach the inner structure of the HII region. We define a set of elliptical annular regions around the central ionizing cluster with an uniformity in their observed properties and consider each annulus as an independent thin shell structur…
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…
(ABRIDGED) We present an analysis of NGC588 based on IFS data with PMAS, together with Spitzer images at 8 mi and 24 mi. The extinction distribution in the optical shows complex structure, with maxima correlating in position with those of the emission at 24 mi and 8 mi. The Ha luminosity absorbed by the dust within the GHIIR reproduces the structure observed in the 24 mi image, supporting the use of this band as a tracer of recent star formation. A velocity difference of ~50 km/s was measured between the areas of high and low surface brightness, which would be expected if NGC588 were an evolve…
We present a photometric estimation of the distance and reddening values to the dwarf irregular galaxy NGC 1156, which is one of the best targets to study the isolated dwarf galaxies in the nearby universe. We have used the imaging data sets of the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) High Resolution Channel (HRC) of the central region of NGC 1156 (26" X 29") available in the HST archive for this study. From the (U-B, B-V) color-color diagram, we first estimate the total (foreground + internal) reddening toward NGC 1156 of E(B-V) =0.35 +/- 0.05 mag, whereas only the f…
Combining Ha and IRAC images of the nearby spiral galaxy NGC 628, we find that between 30-43% of its 8um dust emission is not related to recent star formation. Contributions from dust heated by young stars are separated by identifying HII regions in the Ha map and using these areas as a mask to determine the 8um dust emission that must be due to heating by older stars. Corrections are made for sub-detection-threshold HII regions, photons escaping from HII regions and for young stars not directly associated to HII regions (i.e. 10-100 Myr old stars). A simple model confirms this amount of 8um e…
Context. Outflows powered by the injection of kinetic energy from massive stars can strongly affect the chemical evolution of galaxies, in particular of dwarf galaxies, as their lower gravitational potentials enhance the chance of a galactic wind. Aims. We therefore performed a detailed kinematic analysis of the neutral and ionised gas components in the nearby star-forming irregular dwarf galaxy NGC 4861. Similar to a recently published study of NGC 2366, we want to make predictions about the fate of the gas and to discuss some general issues about this galaxy. Methods. Fabry-Perot interferome…
We present Integral Field Spectroscopy (IFS) of NGC 595, one of the most luminous HII regions in M33. This type of observations allows studying the variation of the principal emission-line ratios across the surface of the nebula. At each position of the field of view, we fit the main emission-line features of the spectrum within the spectral range 3650-6990A, and create maps of the principal emission-line ratios for the total surface of the region. The extinction map derived from the Balmer decrement and the absorbed H-alpha luminosity show good spatial correlation with the 24 micron emission …
(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…
On the basis of a new photometric analysis of the Local Group dwarf irregular galaxy NCG 6822 based on observations obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope, we have obtained a new estimate of the extinction of two fields located in the southeast region of the galaxy. Because of significant differences in the distance estimates to NGC 6822 available in literature, we decided to provide an independent determination of the distance to this galaxy based on an updated and self-consistent theoretical calibration of the tip of the red giant branch brightness. …
The goal of the present study is to establish the physical origin of dust heating and emission based on radiation transfer models, which self-consistently connect the emission components from diffuse dust and the dust in massive star forming regions. NGC 4214 is a nearby dwarf galaxy with a large set of ancillary data, ranging from the ultraviolet (UV) to radio, including maps from SPITZER, HERSCHEL and detections from PLANCK. We mapped this galaxy with MAMBO at 1.2 mm at the IRAM 30 m telescope. We extract separate dust emission components for the HII regions (plus their associated PDRs on pc…
We survey four nearby irregular galaxies for radio supernova remnants (SNRs) using deep (1 sigma ~ 20 microJy), high resolution (~20 pc) VLA continuum data at 20, 6, and 3.6 cm. We identify discrete sources in these galaxies and use radio spectral indices and H alpha images to categorize them as SNRs, H II regions, or background radio galaxies. Our classifications are generally in good agreement agreement with the literature. We identify a total of 43 SNR candidates: 23 in NGC 1569, 7 in NGC 4214, 5 in NGC 2366, and 8 in NGC 4449. Only one SNR--the well-studied object J1228+441 in NGC 4449--is…
Tidal debris which are rich in HI gas, formed in interacting and merging systems, are suitable laboratories to study star formation outside galaxies. Recently, several such systems were observed, which contained many young star forming regions outside the galaxies. In previous works, we have studied young star forming regions outside galaxies in different systems with optical and/or gaseous tidal debris, all of them with available archive GALEX/UV images, in order to understand how often they occur and in which type of environments. In this paper we searched for star forming regions around the…
(abridged) NGC 1569 is a nearby dwarf irregular galaxy which underwent an intense burst of star formation 10 to 40 Myr ago. We present observations that reach surface brightnesses two to eighty times fainter than previous radio continuum observations and the first radio continuum polarization observations. These observations allow us to probe the relationship of the magnetic field of NGC 1569 to the rest of its interstellar medium. We confirm the presence of an extended radio continuum halo at 20 cm and see for the first time the radio continuum feature associated with the western Halpha arm a…
