Kinematics of gas and stars in circumnuclear star-forming regions of early type spirals

(Abbr.) We present high resolution (R~20000) spectra in the blue and the far red of cicumnuclear star-forming regions (CNSFRs) in three early type spirals (NGC3351, NGC2903 and NGC3310) which have allowed the study of the kinematics of stars and ionized gas in these structures and, for the first time, the derivation of their dynamical masses for the first two. In some cases these regions, about 100 to 150 pc in size, are seen to be composed of several individual star clusters with sizes between 1.5 and 4.9 pc estimated from Hubble Space Telescope (HST) images. The stellar dispersions have been obtained from the Calcium triplet (CaT) lines at $\lambda\lambda$ 8494,8542,8662 \AA, while the gas velocity dispersions have been measured by Gaussian fits to the H$\beta$ and [OIII] $\lambda\lambda$ 5007 \AA lines on the high dispersion spectra. Values of the stellar velocity dispersions are between 30 and 68 km/s. We apply the virial theorem to estimate dynamical masses of the clusters, assuming that systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 10$^7$ to 10$^8$ solar masses for the whole CNSFRs. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km/s with the H$\beta$ emission lines being narrower than both the stellar lines and the [OIII] $\lambda\lambda$ 5007 \AA lines. The twice ionized oxygen, on the other hand, shows velocity dispersions comparable to those shown by stars, in some cases, even larger. We have found indications of the presence of two different kinematical components in the ionized gas of the regions...Comment: 4 pages, proceeding of the meeting "Young massive star clusters - Initial conditions and environments", Granada, Spain, 200

Integral field spectroscopy of HII regions in M33

Integral field spectroscopy (IFS) is presented for star forming regions in M33. A central area of 300 x 500 pc^2 and the external HII region IC 132, at a galactocentric distance {\sim} 19arcmin (4.69 kpc) were observed with the Potsdam Multi Aperture Spectrophotometer (PMAS) instrument at the 3.5 m telescope of the Calar Alto Hispano- Alem\'an observatory (CAHA). The spectral coverage goes from 3600 A to 1{\mu}m to include from [OII]{\lambda}3727 A to the near infrared lines required for deriving sulphur electron temperature and abundance diagnostics. Local conditions within individual HII regions are presented in the form of emission line fluxes and physical conditions for each spatial resolution element (spaxel) and for segments with similar H{\alpha} surface brightness. A clear dichotomy is observed when comparing the central to outer disc HII regions. While the external HII region has higher electron temperature plus larger H{\beta} equivalent width, size and excitation, the central region has higher extinction and metal content. The dichotomy extends to the BPT diagnostic diagrams that show two orthogonal broad distributions of points. By comparing with pseudo-3D photoionization models we conclude that the bulk observed differences are probably related to a different ionization parameter and metallicity. Wolf-Rayet features are detected in IC 132, and resolved into two concentrations whose integrated spectra were used to estimate the characteristic number of WR stars. No WR features were detected in the central HII regions despite their higher metallicity.Comment: 72 pages, 37 figure

The temperature and ionization structure of the emitting gas in H II galaxies: implicatins for the accuracy of abundance determinations

This is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. Hägele, G.F., Pérez-Montero, E., Díaz, A.I., Terlevich, E. and R. Terlevich. The temperature and ionization structure of the emitting gas in H II galaxies: implicatins for the accuracy of abundance determinations. Monthly Notices of the Royal Astronomical Society 372 (2006): 293-31

The circumnuclear environment of the peculiar galaxy NGC 3310

Gas and star velocity dispersions have been derived for eight circumnuclear star-forming regions (CNSFRs) and the nucleus of the spiral galaxy NGC 3310 using high-resolution spectroscopy in the blue and far red. Stellar velocity dispersions have been obtained from the Ca ii triplet in the near-IR, using cross-correlation techniques, while gas velocity dispersions have been measured by Gaussian fits to the Hβ λ4861 Å and [O iii] λ5007 Å emission lines.The CNSFR stellar velocity dispersions range from 31 to 73 km s-1. These values, together with the sizes measured on archival Hubble Space Telescope images, yield upper limits to the dynamical masses for the individual star clusters between 1.8 and 7.1 × 106 M⊙, for the whole CNSFR between 2 × 107 and 1.4 × 108 M⊙, and 5.3 × 107 M⊙, for the nucleus inside the inner 14.2 pc. The masses of the ionizing stellar population responsible for the H ii region gaseous emission have been derived from their published Hα luminosities and are found to be between 8.7 × 105 and 2.1 × 106 M⊙ for the star-forming regions and 2.1 × 105 M⊙ for the galaxy nucleus; they therefore constitute between 1 and 7 per cent of the total dynamical mass.The ionized gas kinematics is complex; two different kinematical components seem to be present as evidenced by different linewidths and Doppler shifts.Facultad de Ciencias Astronómicas y Geofísica

On the derivation of dynamical masses of the stellar clusters in the circumnuclear region of NGC 2903

Gas and star velocity dispersions have been derived for four circumnuclear star-forming regions (CNSFRs) and the nucleus of the spiral galaxy NGC 2903 using high-resolution spectroscopy in the blue and far red. Stellar velocity dispersions have been obtained from the Ca ii triplet lines at λλ 8494, 8542, 8662 Å, using cross-correlation techniques, while gas velocity dispersions have been measured by Gaussian fits to the Hβ λ 4861 Å line. The CNSFRs, with sizes of about 100 to 150 pc in diameter, show a complex structure at the Hubble Space Telescope (HST) resolution, with a good number of subclusters with linear diameters between 3 and 8 pc. Their stellar velocity dispersions range from 39 to 67 km s-1. These values, together with the sizes measured on archival HST images, yield upper limits to the dynamical masses for the individual star clusters between 1.8 and 8.7 × 106 M⊙ and upper limits to the masses for the whole CNSFR between 4.9 × 106 and 4.3 × 107 M⊙. The masses of the ionizing stellar population responsible for the H ii region gaseous emission have been derived from their published Hα luminosities and are found to be between 1.9 and 2.5 × 10 6 M⊙ for the star-forming regions, and 2.1 × 105 M⊙ for the galaxy nucleus, therefore constituting between 1 and 4 per cent of the total dynamical mass. In the CNSFR, star and gas velocity dispersions are found to differ by about 20 km s-1 with the Hβ lines being narrower than both the stellar lines and the [O iii] λ 5007 Å lines. The ionized gas kinematics are complex; two different kinematical components seem to be present as evidenced by different widths and Doppler shifts. The line profiles in the spectra of the galaxy nucleus, however, are consistent with the presence of a single component with radial velocity and velocity dispersion close to those measured for the stellar absorption lines. The presence and reach of two distinct components in the emission lines in ionized regions and the influence that this fact could have on the observed line ratios are of major interest for several reasons, among others, the classification of the activity in the central regions of galaxies, the inferences about the nature of the source of ionization for the two components and the derivation of the gaseous chemical abundances.Facultad de Ciencias Astronómicas y Geofísica

The circumnuclear environment of the peculiar galaxy NGC 3310

Gas and star velocity dispersions have been derived for eight circumnuclear star-forming regions (CNSFRs) and the nucleus of the spiral galaxy NGC 3310 using high-resolution spectroscopy in the blue and far red. Stellar velocity dispersions have been obtained from the Ca ii triplet in the near-IR, using cross-correlation techniques, while gas velocity dispersions have been measured by Gaussian fits to the Hβ λ4861 Å and [O iii] λ5007 Å emission lines.The CNSFR stellar velocity dispersions range from 31 to 73 km s-1. These values, together with the sizes measured on archival Hubble Space Telescope images, yield upper limits to the dynamical masses for the individual star clusters between 1.8 and 7.1 × 106 M⊙, for the whole CNSFR between 2 × 107 and 1.4 × 108 M⊙, and 5.3 × 107 M⊙, for the nucleus inside the inner 14.2 pc. The masses of the ionizing stellar population responsible for the H ii region gaseous emission have been derived from their published Hα luminosities and are found to be between 8.7 × 105 and 2.1 × 106 M⊙ for the star-forming regions and 2.1 × 105 M⊙ for the galaxy nucleus; they therefore constitute between 1 and 7 per cent of the total dynamical mass.The ionized gas kinematics is complex; two different kinematical components seem to be present as evidenced by different linewidths and Doppler shifts.Facultad de Ciencias Astronómicas y Geofísica

Implications of the kinematical structure of circumnuclear star-forming regions on their derived properties

We reviewthe results of high-dispersion spectroscopy of 17 circumnuclear star-forming regions (CNSFRs) in 3 nearby early spiral galaxies, NGC 2903, NGC 3310 and NGC 3351. We findthat single-Gaussian fitting to the Hβ and [O III]λ5007 Å line profiles results in velocity dispersions around 32 and 52 km s-1, respectively, while the IR Ca II triplet cross-correlation technique provides stellar velocity dispersion values close to 50 km s-1. Even though multiple kinematical components are present, the relation between gas velocity dispersion and Balmer emission line luminosity (L-σ relation) reproduces the correlation for disc giant HII regions albeit with a larger scatter. The scatter in the L-σ relation is considerably reduced when theoretical evolutionary corrections are applied suggesting that an age range is present in the sample of CNSFRs. To analyse the observed complex profiles, we performed multiple Gaussian component fits to the Hβ and [O III]λ5007 Å lines obtaining optimal fits with two Gaussians of different widths. These best fits indicate that the narrower component has average velocity dispersion close to 23 km s-1 while the broader component shows average values in the range 50-60 km s-1 for both lines, close to the observed stellar velocity dispersions. The fluxes of the broad and narrow Hβ components are similar. This is not the case for [O III]λ5007 Å for which the broad components have higher fluxes than the narrow ones, thus producing a clear segregation in their [OIII]/Hβ ratios. We suggest a possible scenario for understanding the behaviour of CNSFRs in the L-σ and σgas-σ* diagrams involving aninner gaseous disc responsible for the narrow component of the emission lines. Our main conclusion is that the presence of different kinematical components with similar total fluxes in the emission line spectrum of CNSFRs raises important doubts regarding the properties of the ionized gas derived from global line ratios obtained with low-resolution spectroscopy in star-forming regions in the central regions of early-type galaxies. Given the ubiquity of these star-forming systems, ionized gas analyses should be done preferably from high-dispersion spectra with high spatial resolution.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

The circumnuclear environment of the peculiar galaxy NGC 3310

Gas and star velocity dispersions have been derived for eight circumnuclear star-forming regions (CNSFRs) and the nucleus of the spiral galaxy NGC3310 using high resolution spectroscopy in the blue and far red. Stellar velocity dispersions have been obtained from the CaII triplet in the near-IR, using cross-correlation techniques, while gas velocity dispersions have been measured by Gaussian fits to the Hb 4861A and [OIII]5007A emission lines. The CNSFRs stellar velocity dispersions range from 31 to 73 km/s. These values, together with the sizes measured on archival HST images, yield upper limits to the dynamical masses for the individual star clusters between 1.8 and 7.1 x 10$^6$ M$_\odot$, for the whole CNSFR between 2 x 10$^7$ and 1.4 x 10$^8$ M$_\odot$, and 5.3 x 10$^7$ M$_\odot$ for the nucleus inside the inner 14.2 pc. The masses of the ionizing stellar population responsible for the HII region gaseous emission have been derived from their published Ha luminosities and are found to be between 8.7 x 10$^5$ and 2.1 x 10$^6$ M$_\odot$ for the star-forming regions, and 2.1 x 10$^5$ M$_\odot$ for the galaxy nucleus; they therefore constitute between 1 and 7 per cent of the total dynamical mass. The ionized gas kinematics is complex; two different kinematical components seem to be present as evidenced by different line widths and Doppler shifts.Comment: 24 pages, accepted by MNRA

High-velocity blueshifted Fe II absorption in the dwarf star-forming galaxy PHL 293B: evidence for a wind driven supershell?

X-shooter and WHT-ISIS spectra of the star-forming galaxy PHL 293B also known as A2228- 00 and SDSS J223036.79-000636.9 are presented in this paper. We find broad (FWHM = 1000 km s-1) and very broad (FWZI = 4000 km s-1) components in the Balmer lines, narrow absorption components in the Balmer series blueshifted by 800 km s-1, previously undetected Fe II multiplet (42) absorptions also blueshifted by 800 km s-1, IR CaII triplet stellar absorptions consistent with [Fe/H] < -2.0 and no broad components or blueshifted absorptions in the He I lines. Based on historical records, we found no optical variability at the 5s level of 0.02 mag between 2005 and 2013 and no optical variability at the level of 0.1 mag for the past 24 yr. The lack of variability rules out transient phenomena like luminous blue variables or Type IIn supernovae as the origin of the blueshifted absorptions of HI and Fe II. The evidence points to either a young and dense expanding supershell or a stationary cooling wind, in both cases driven by the young cluster wind.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica

Abundance determination of multiple star-forming regions in the H II galaxy SDSS J165712.75+321141.4

We analyse high signal-to-noise ratio spectrophotometric observations acquired simultaneously with TWIN, a double-arm spectrograph, from 3400 to 10400 Å of three star-forming regions in the H II galaxy SDSS J165712.75+321141.4. We have measured four line temperatures -Te([O III]), Te([S III]), Te([O II]) and Te([S II]) - with high-precision, rms errors of the order of 2, 5, 6 and 6 per cent, respectively, for the brightest region, and slightly worse for the other two. The temperature measurements allowed the direct derivation of ionic abundances of oxygen, sulphur, nitrogen, neon and argon. We have computed cloudy tailor-made models which reproduce the O2+-measured thermal and ionic structures within the errors in the three knots, with deviations of only 0.1 dex in the case of O+ and S2+ ionic abundances. In the case of the electron temperature and the ionic abundances of S+/H+, we find major discrepancies which could be the consequence of the presence of colder diffuse gas. The star formation history derived using starlight shows a similar age distribution of the ionizing population among the three star-forming regions. This fact suggests a similar evolutionary history which is probably related to the process of interaction with a companion galaxy that triggered the star formation in the different regions almost at the same time. The hardness of the radiation field mapped through the use of the softness parameter η is the same within the observational errors for all three regions, implying that the equivalent effective temperatures of the radiation fields are very similar for all the studied regions of the galaxy, in spite of some small differences in the ionization state of different elements. Regarding the kinematics of the galaxy, the gas rotation curve shows a deviation from the circular motion probably due either to an interaction process or to an expanding bubble or shell of the ionized gas approaching us. A dynamical mass of 2.5×1010M⊙ is derived from the rotation curve.Facultad de Ciencias Astronómicas y Geofísica