Deep H? survey of the Milky Way (original) (raw)
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Monthly Notices of the Royal Astronomical Society, 2015
We have observed 10 interacting galaxy pairs using the Fabry-Perot interferometer GHαFaS (Galaxy Hα Fabry-Perot system) on the 4.2m William Herschel Telescope (WHT) at the Observatorio del Roque de los Muchachos, La Palma. We present here the Hα surface brightness, velocity and velocity dispersion maps for the 10 systems we have not previously observed using this technique, as well as the physical properties (sizes, Hα luminosities and velocity dispersion) of 1259 Hii regions from the full sample. We also derive the physical properties of 1054 Hii regions in a sample of 28 isolated galaxies observed with the same instrument in order to compare the two populations of Hii regions. We find a population of the brightest Hii regions for which the scaling relations, for example the relation between the Hα luminosity and the radius, are clearly distinct from the relations for the regions of lower luminosity. The regions in this bright population are more frequent in the interacting galaxies. We find that the turbulence, and also the star formation rate, are enhanced in the Hii regions in the interacting galaxies. We have also extracted the Hα equivalent widths for the Hii regions of both samples, and we have found that the distribution of Hii region ages coincides for the two samples of galaxies. We suggest that the SFR enhancement is brought about by gas flows induced by the interactions, which give rise to gravitationally bound gas clouds which grow further by accretion from the flowing gas, producing conditions favourable to star formation.
The vertical structure and kinematics of HI in spiral galaxies
2000
We discuss the distribution and kinematics of neutral hydrogen in the halos of spiral galaxies. We focus in particular on new results obtained for the nearby Sc galaxy NGC 2403 which have revealed the presence of extended HI emission (here referred to as the 'beard') at anomalous velocities with respect to the 'cold' HI disk. Modeling shows that this component has a mass of about 1/10 of the total HI mass and is probably located in the halo region. Its kinematics differs from that of the thin HI disk: it rotates more slowly and shows radial inflow. The origin of this anomalous gas component is unknown. It could be the result of a galactic fountain or of accretion of extragalactic 'primordial' gas.
Age, size, and position of H ii regions in the Galaxy
Astronomy & Astrophysics, 2014
Aims. This work aims at improving the current understanding of the interaction between H ii regions and turbulent molecular clouds. We propose a new method to determine the age of a large sample of OB associations by investigating the development of their associated H ii regions in the surrounding turbulent medium. Methods. Using analytical solutions, one-dimensional (1D), and three-dimensional (3D) simulations, we constrained the expansion of the ionized bubble depending on the turbulent level of the parent molecular cloud. A grid of 1D simulations was then computed in order to build isochrone curves for H ii regions in a pressure-size diagram. This grid of models allowed to date large sample of OB associations and was used on the H ii Region Discovery Survey (HRDS). Results. Analytical solutions and numerical simulations showed that the expansion of H ii regions is slowed down by the turbulence up to the point where the pressure of the ionized gas is in a quasi-equilibrium with the turbulent ram pressure. Based on this result, we built a grid of 1D models of the expansion of H ii regions in a profile based on Larson laws. The 3D turbulence is taken into account by an effective 1D temperature profile. The ages estimated by the isochrones of this grid agree well with literature values of well-known regions such as Rosette, RCW 36, RCW 79, and M16. We thus propose that this method can be used to give ages of young OB associations through the Galaxy such as the HRDS survey and also in nearby extra-galactic sources.
The kinematics and morphology of the Hi in gas-poor galaxies
New Astronomy Reviews, 2007
We present the results of deep Westerbork Synthesis Radio Telescope observations of the neutral hydrogen in 12 nearby elliptical and lenticular galaxies selected from a representative sample of nearby galaxies that were studied earlier at optical wavelengths with the integral-field spectrograph sauron. The observed objects are field galaxies, or (in two cases) are located in poor-group environments. We detect HI in 70% of the galaxies. This detection rate is much higher than in previous, shallower single-dish surveys, and is similar to that for the ionised gas. The results suggest that at faint detection levels the presence of HI is a relatively common characteristic of field early-type galaxies. The presence of regular disc-like structures is as common as HI in offset clouds and tails. All galaxies where HI is detected also contain ionised gas, whereas no HI is found around galaxies without ionised gas. Galaxies with regular HI discs tend to have strong emission from ionised gas. In these cases, the similar kinematics of the neutral hydrogen and ionised gas suggest that they form one structure. We do not find a trend between the presence of HI and the global age of the stellar population or with the global dynamical characteristics of the galaxies. If fast and slow rotators represent the relics of different formation paths, this does not appear in the presence and characteristics of the HI. The links observed between the large-scale gas and the characteristics on the nuclear scale (e.g. the presence of kinematically decoupled cores and radio continuum emission), suggest that for the majority of the cases the gas is acquired through merging, but the lack of correlation with the stellar-population age suggests that smooth, cold accretion could be an alternative scenario, at least in some galaxies. In either case, the data suggest that early-type galaxies continue to build-up their mass to the present.
Monthly Notices of the Royal Astronomical Society, 2012
We present the ATLAS 3D H I survey of a volume-limited, complete sample of 166 nearby early-type galaxies (ETGs) brighter than M K = −21.5. The survey is mostly based on data taken with the Westerbork Synthesis Radio Telescope, which enables us to detect H I down to 5 × 10 6-5 × 10 7 M within the survey volume. We detect ∼40 per cent of all ETGs outside the Virgo galaxy cluster and ∼10 per cent of all ETGs inside it. This demonstrates that it is common for non-cluster ETGs to host H I. The morphology of the detected gas varies in a continuous way from regular, settled H I discs and rings to unsettled gas distributions (including tidal or accretion tails) and systems of clouds scattered around the galaxy. The majority of the detections consist of H I discs or rings (1/4 of all ETGs outside Virgo) so that if H I is detected in an ETG it is most likely distributed on a settled configuration. These systems come in two main types: small discs [M(H I) < 10 8 M ], which are confined within the stellar body and share the same kinematics of the stars; and large discs/rings [M(H I) up to 5 × 10 9 M ], which extend to tens of kpc from the host galaxy and are in half of the cases kinematically decoupled from the stars.
Observations of Complex H, a High Velocity Cloud Close to the Galactic Plane
2008
Using 21 cm observations of Complex H with the Green Bank Radio Telescope, we have derived its LSR velocity of ˜ 200 km s-1 and an H I mass of 7.5× 107 M&sun;. This gives useful support to the scenario in which the Galactic disk is being built up by the continual accretion of clouds of this type from the intracluster medium of the Local Group. Complex H is detected as shedding a gas tail, and has a shock front at its leading surface, both phenomena attributable to its interaction with the halo gas of the Milky Way.
Giant H ii regions in NGC 7479 and NGC 6070
Monthly Notices of the Royal Astronomical Society, 2000
We present new results from our search for Giant H 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 ii regions. We find that all of them show at least two distinct kinematical components: a relatively narrow feature (between 11 and 22 km s −1 ) and a broader (between 31 and 77 km s −1 ) component. Two of the regions show a complex narrow profile in all ion lines, which can be further split into two components with different radial velocities. Whereas the wing broadening of the overall profile can be fitted with a low-intensity broad component for almost all profiles, in one region it was better reproduced by two separate shell-like wings. We have analysed the impact that the presence of multiple components has on the location of the Hii regions in the log(L) − log(σ) plane. Although the overall distribution confirms the presence of a regression, the precise location of the regions in the plane is strongly dependent on the components derived from the profile fitting.
A Deep Survey of H i –selected Galaxies: The Sample and the Data
The Astrophysical Journal Supplement Series, 1998
In a 21 cm neutral hydrogen survey of approximately 55 deg 2 out to a redshift of cz = 8340 km s −1 , we have identified 75 extragalactic HI sources. These objects comprise a well-defined sample of extragalactic sources chosen by means that are independent of optical surface brightness selection effects. In this paper we describe the Arecibo survey procedures and HI data, follow-up VLA HI observations made of several unusual sources, and Kitt Peak B-, R-, and I-band photometry for nearly all of the galaxies. We have also gathered information for some of the optically detected galaxies within the same search volume. We examine how samples generated by different types of search techniques overlap with selection by HI flux. Only the least massive HI object, which is among the lowest mass HI sources previously found, does not have a clear optical counterpart, but a nearby bright star may hide low surface brightness emission. However the newly-detected systems do have unusual optical properties. Most of the 40 galaxies that were not previously identified in magnitude-limited catalogs appear to be gas-dominated systems, and several of these systems have HI mass-to-light ratios among the largest values ever previously found. These gas-dominated objects also tend to have very blue colors, low surface brightnesses, and no central bulges, which correlate strongly with their relative star-togas content.