arXiv subjects

M. Baes

Publications and source records attributed to M. Baes.

269 records · Page 15Linked to original sources

arXiv2010

Mass models from high-resolution HI data of the dwarf galaxy NGC 1560

We present HI observations performed at the GMRT of the nearby dwarf galaxy NGC 1560. This Sd galaxy is well-known for a distinct "wiggle" in its rotation curve. Our new observations have twice the resolution of the previously published HI data. We derived the rotation curve by taking projection effects into account, and we verified the derived kinematics by creating model datacubes. This new rotation curve is similar to the previously published one: we confirm the presence of a clear wiggle. The main differences are in the innermost ~100 arcsec of the rotation curve, where we find slightly (<~ 5 km/s) higher velocities. Mass modelling of the rotation curve results in good fits using the core-dominated Burkert halo (which however does not reproduce the wiggle), bad fits using the a Navarro, Frenk & White halo, and good fits using MOND (Modified Newtonian Dynamics), which also reproduces the wiggle.

astro-ph.CO↗

arXiv2010

The Herschel Reference Survey

The Herschel Reference Survey is a guaranteed time Herschel key project and will be a benchmark study of dust in the nearby universe. The survey will complement a number of other Herschel key projects including large cosmological surveys that trace dust in the distant universe. We will use Herschel to produce images of a statistically-complete sample of 323 galaxies at 250, 350 and 500 micron. The sample is volume-limited, containing sources with distances between 15 and 25 Mpc and flux limits in the K-band to minimize the selection effects associated with dust and with young high-mass stars and to introduce a selection in stellar mass. The sample spans the whole range of morphological types (ellipticals to late-type spirals) and environments (from the field to the centre of the Virgo Cluster) and as such will be useful for other purposes than our own. We plan to use the survey to investigate (i) the dust content of galaxies as a function of Hubble type, stellar mass and environment, (ii) the connection between the dust content and composition and the other phases of the interstellar medium and (iii) the origin and evolution of dust in galaxies. In this paper, we describe the goals of the survey, the details of the sample and some of the auxiliary observing programs that we have started to collect complementary data. We also use the available multi-frequency data to carry out an analysis of the statistical properties of the sample.

astro-ph.CO↗

arXiv2009

The Herschel ATLAS

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 510 square degrees of the extragalactic sky, four times larger than all the other Herschel surveys combined, in five far-infrared and submillimetre bands. We describe the survey, the complementary multi-wavelength datasets that will be combined with the Herschel data, and the six major science programmes we are undertaking. Using new models based on a previous submillimetre survey of galaxies, we present predictions of the properties of the ATLAS sources in other wavebands.

astro-ph.CO↗

arXiv2009

Studying the spectral properties of Active Galactic Nuclei in the JWST era

The James Webb Space Telescope (JWST), due to launch in 2014, shall provide an unprecedented wealth of information in the near and mid-infrared wavelengths, thanks to its high-sensitivity instruments and its 6.5 m primary mirror, the largest ever launched into space. NIRSpec and MIRI, the two spectrographs onboard JWST, will play a key role in the study of the spectral features of Active Galactic Nuclei in the 0.6-28 micron wavelength range. This talk aims at presenting an overview of the possibilities provided by these two instruments, in order to prepare the astronomical community for the JWST era.

astro-ph.CO↗

arXiv2009

A multi-wavelength survey of AGN in the XMM-LSS field: I. Quasar selection via the KX technique

AIMS: We present a sample of candidate quasars selected using the KX-technique. The data cover 0.68 deg^2 of the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey area where overlapping multi-wavelength imaging data permits an investigation of the physical nature of selected sources. METHODS: The KX method identifies quasars on the basis of their optical (R and z') to near-infrared (Ks) photometry and point-like morphology. We combine these data with optical (u*,g'r',i',z') and mid-infrared (3.6-24 micron) wavebands to reconstruct the spectral energy distributions (SEDs) of candidate quasars. RESULTS: Of 93 sources selected as candidate quasars by the KX method, 25 are classified as quasars by the subsequent SED analysis. Spectroscopic observations are available for 12/25 of these sources and confirm the quasar hypothesis in each case. Even more, 90% of the SED-classified quasars show X-ray emission, a property not shared by any of the false candidates in the KX-selected sample. Applying a photometric redshift analysis to the sources without spectroscopy indicates that the 25 sources classified as quasars occupy the interval 0.7 < z < 2.5. The remaining 68/93 sources are classified as stars and unresolved galaxies.

astro-ph↗

arXiv2008

LABOCA and MAMBO-2 imaging of the dust ring of the Sombrero galaxy (NGC 4594)

The Sombrero galaxy (NGC 4594) is an Sa galaxy with a symmetric dust ring. We have used the Large APEX BOlometer CAmera (LABOCA) at 870 micron and the MAx-Planck Millimeter BOlometer (MAMBO-2) at 1.2 mm to detect the dust ring for the first time at submillimetre and millimetre wavelengths. We have constructed a model of the galaxy to separate the active galactic nucleus (AGN) and dust ring components. The ring radius at both 870 micron and 1.2 mm agrees well with the radius determined from optical absorption and atomic gas studies. The spectral energy distribution of the ring is well fitted by a single grey-body with dust emissivity index beta=2 and a dust temperature T_d=18.4 K. The dust mass of the ring is found to be 1.6\pm0.2x10^7Msun which, for a Galactic gas-to-dust ratio, implies a gas mass that is consistent with measurements from the literature.

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arXiv2007

The Arecibo Galaxy Environment Survey: II. A HI view of the Abell cluster 1367 and its outskirts

We present 21 cm HI line observations of 5x1 square degrees centered on the local Abell cluster 1367 obtained as part of the Arecibo Galaxy Environment Survey. One hundred sources are detected (79 new HI measurements and 50 new redshifts), more than half belonging to the cluster core and its infalling region. Combining the HI data with SDSS optical imaging we show that our HI selected sample follows scaling relations similar to the ones usually observed in optically selected samples. Interestingly all galaxies in our sample appear to have nearly the same baryon fraction independently of their size, surface brightness and luminosity. The most striking difference between HI and optically selected samples resides in their large scale distribution: whereas optical and X-ray observations trace the cluster core very well, in HI there is almost no evidence of the presence of the cluster. Some implications on the determination of the cluster luminosity function and HI distribution for samples selected at different wavelength are also discussed.

astro-ph↗

arXiv2007

VSOP: The Variable Star One-shot Project I. Project presentation and first data release

The Variable Star One-shot Project (VSOP) is aimed at (1) providing the variability type and spectral type of all unstudied variable stars, (2) process, publish, and make the data available as automatically as possible, and (3) generate serendipitous discoveries. This first paper describes the project itself, the acquisition of the data, the dataflow, the spectroscopic analysis and the on-line availability of the fully calibrated and reduced data. We also present the results on the 221 stars observed during the first semester of the project. We used the high-resolution echelle spectrographs HARPS and FEROS in the ESO La Silla Observatory (Chile) to survey known variable stars. Once reduced by the dedicated pipelines, the radial velocities are determined from cross correlation with synthetic template spectra, and the spectral types are determined by an automatic minimum distance matching to synthetic spectra, with traditional manual spectral typing cross-checks. The variability types are determined by manually evaluating the available light curves and the spectroscopy. In the future, a new automatic classifier, currently being developed by members of the VSOP team, based on these spectroscopic data and on the photometric classifier developed for the COROT and Gaia space missions, will be used. We confirm or revise spectral types of 221 variable stars from the GCVS. We identify 26 previously unknown multiple systems, among them several visual binaries with spectroscopic binary individual components. We present new individual results for the multiple systems V349 Vel and BC Gru, for the composite spectrum star V4385 Sgr, for the T-Tauri star V1045 Sco, and for DM Boo which we re-classify as a BY Draconis variable. The complete data release can be accessed via the VSOP web site.

astro-ph↗

arXiv2007

Dynamical models with a general anisotropy profile

Both numerical simulations and observational evidence indicate that the outer regions of galaxies and dark matter haloes are typically mildly to significantly radially anisotropic. The inner regions can be significantly non-isotropic, depending on the dynamical formation and evolution processes. In an attempt to break the lack of simple dynamical models that can reproduce this behaviour, we explore a technique to construct dynamical models with an arbitrary density and an arbitrary anisotropy profile. We outline a general construction method and propose a more practical approach based on a parameterized anisotropy profile. This approach consists of fitting the density of the model with a set of dynamical components, each of which have the same anisotropy profile. Using this approach we avoid the delicate fine-tuning difficulties other fitting techniques typically encounter when constructing radially anisotropic models. We present a model anisotropy profile that generalizes the Osipkov-Merritt profile, and that can represent any smooth monotonic anisotropy profile. Based on this model anisotropy profile, we construct a very general seven-parameter set of dynamical components for which the most important dynamical properties can be calculated analytically. We use the results to look for simple one-component dynamical models that generate simple potential-density pairs while still supporting a flexible anisotropy profile. We present families of Plummer and Hernquist models in which the anisotropy at small and large radii can be chosen as free parameters. We also generalize these two families to a three-parameter family that self-consistently generates the set of Veltmann potential-density pairs. (Abridged...)

astro-ph↗

arXiv2007

The Variable Star One-shot Project, and its little child: Wikimbad

The Variable Star One-shot Project (VSOP) aimed at providing to the world-wide stellar community the necessary one-shot spectrum of unstudied variable stars, too often classified as such by an analysis of photometric data only. The VSOP has established an new kind of observational model, where all steps from observations to spectral analysis, are automatized (or are underway to be fully automatized). The project is centralized on a collaborative wiki website. The VSOP operational model is very successful, data is continously flowing and being analyszed, and VSOP is now a worldwide open collaboration of people with very different and complementary skills and expertise. The idea of a central wiki website has been extended by one of us to propose a new service to the whole astronomical community, called Wikimbad. Wikimbad is an open wiki website aimed at collecting, organizing and making publicly available all kind of reduced and published astronomical data. Its strengths and a comparison with the Virtual Observatory are discussed. See: http://vsop.sc.eso.org and http://wikimbad.org

astro-ph↗

arXiv2007

Metallicity and age gradients in round elliptical galaxies

We probe the stellar population age and metallicity distributions in nearby elliptical galaxies over the largest extension to date. Long-slit spectroscopy is made by using the spectrograph SCORPIO of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciencies. The Lick indices H-beta, Mg b, Fe5270, and Fe5335 are calculated along the slit up to radii of 1.3 to 3r_e in 4 galaxies and up to 0.5r_e in the fifth one. The comparison with evolutionary synthesis models of simple stellar populations allows us to disentangle age and metallicity and to measure both. We have found that the mean stellar age is constant along the radius only in one galaxy out of 5. The other 4 galaxies demonstrate quite different behaviour of the mean stellar age: the outer parts are older than the centres in 3 cases and younger - in one case. The metallicity gradients cannot be approximated by a single power law over the full radial extension in 4 galaxies of 5. The inner metallicity gradients within 0.5r_e are all rather steep, steeper than -0.4 metallicity dex per radius dex, and are inconsistent with the origin of the elliptical galaxies by a major merger.

astro-ph↗

arXiv2006

The Arecibo Galaxy Environment Survey: Precursor Observations of the NGC 628 group

The Arecibo Galaxy Environment Survey (AGES) is one of several HI surveys utilising the new Arecibo L-band Feed Array (ALFA) fitted to the 305m radio telescope at Arecibo. The survey is specifically designed to investigate various galactic environments to higher sensitivity, higher velocity resolution and higher spatial resolution than previous fully sampled, 21 cm multibeam surveys. The emphasis is on making detailed observations of nearby objects although the large system bandwidth (100 MHz) will allow us to quantify the HI properties over a large instantaneous velocity range. In this paper we describe the survey and its goals and present the results from the precursor observations of a 5 degree x 1 degree region containing the nearby (~10 Mpc) NGC 628 group. We have detected all the group galaxies in the region including the low mass (M{HI}~10^7Mo) dwarf, dw0137+1541 (Briggs, 1986). The fluxes and velocities for these galaxies compare well with previously published data. There is no intra-group neutral gas detected down to a limiting column density of 2x10^{18}cm^{-2}. In addition to the group galaxies we have detected 22 galaxies beyond the NGC 628 group, 9 of which are previously uncatalogued.(Abridged)

astro-ph↗

arXiv2005

The HI content of Fornax dwarf elliptical galaxies: FCC032 and FCC336

We present HI 21cm line observations, obtained with the Australia Telescope Compact Array, of two dwarf elliptical galaxies (dEs) in the Fornax cluster: FCC032 and FCC336. The optical positions and velocities of these galaxies place them well within the Fornax cluster. FCC032 was detected at the 3sigma significance level with a total HI flux density of 0.66+-0.22 Jy km s^-1 or an HI mass of 5.0+-1.7 10^7 h_75^-2 M_sun. Based on our deep Halpha+[NII] narrow-band images, obtained with FORS2 mounted on the VLT, this dE was already known to contain 600-1800 h_75^-2 M_sun of ionised Hydrogen (depending on the relative strengths of the Halpha and [NII] emission lines). Hence, this is the first study of the complex, multi-phase interstellar medium of a dE outside the Local Group. FCC336 was detected at the same significance level: 0.37+-0.10 Jy km s^-1 or a total HI mass of 2.8+-0.7 10^7 h_75^-2,M_sun. Using a compilation of HI data of dwarf galaxies, we find that the observed high HI-mass boundary of the distribution of dIrrs, BCDs, and dEs in a log(L_B) versus log (M_HI) diagram is in good agreement with a simple chemical evolution model with continuous star formation. The existence of many gas-poor dEs (undetected at 21cm) suggest that the environment (or more particularly, a galaxy's orbit within a cluster) also plays a crucial role in determining the amount of gas in present-day dEs. E.g., FCC032 and FCC336 are located in the sparsely populated outskirts of the Fornax cluster. This is in agreement with HI surveys of dEs in the Virgo Cluster and an Halpha survey of the Fornax Cluster, which also tend to place gas-rich dwarf galaxies in the cluster periphery.

astro-ph↗

arXiv2004

The Dwarf LSB Galaxy Population of the Virgo Cluster II. Colours and HI line observations

In order to investigate the nature of dwarf Low Surface Brightness (LSB) galaxies we have undertaken a deep B and I band CCD survey of a 14 sq degree strip in the Virgo Cluster and applied a Fourier convolution technique to explore its dwarf galaxy population down to a central surface brightness of 26 B mag/sq arcsec and a total absolute B mag of ~ -10. In this paper we carry out an analysis of their morphology, (B-I) colours and atomic hydrogen content. We compare these properties with those of dwarf galaxies in other environments to try and assess how the cluster environment has influenced their evolution. Field dwarfs are generally of a more irregular morphology, are bluer and contain relatively more gas. We assess the importance that various physical processes have on the evolution of cluster dwarf galaxies (ram pressure stripping, tidal interactions, supernova driven gas loss). We suggest that enhanced star formation triggered by tidal interactions is the major reason for the very different general properties of cluster dwarfs: they have undergone accelerated evolution.

astro-ph↗

arXiv2004

A search for low surface brightness dwarf galaxies in different environments

According to the Cold Dark Matter (CDM) hierarchical clustering theory of galaxy and large scale structure formation, there should be numerous low mass dark matter haloes present in the Universe today. If these haloes contain sufficient stars they should be detectable as low luminosity stellar systems or dwarf galaxies. We have previously described a new detection method for faint low surface brightness objects and shown that there are relatively large numbers of very faint dwarf galaxies in the nearby Virgo cluster. In this paper we present results from a similar survey carried out on the Millennium Galaxy strip which runs along the celestial equator and samples a very different galaxy environment. We show that the dwarf-to-giant galaxy number ratio along this strip ranges from 0.7:1 to, at most, 6:1, corresponding to a flat luminosity function (alpha approx -0.8 to -1.0). This is very different to our value of 20:1 for the Virgo cluster. There is no population of low surface brightness dwarf galaxies in the field that have gone undetected by the redshift surveys. This result is exactly opposite to what CDM models predict for the environmental dependence of the dark matter mass function which is that there are proportionally more small dark matter haloes in lower density environments.

astro-ph↗

arXiv2003

A multi-beam HI survey of the Virgo Cluster - two isolated HI clouds ?

We have carried out a fully sampled large area ($4^{\circ} \times 8^{\circ}$) 21cm \HI line survey of part of the Virgo cluster using the Jodrell Bank multi-beam instrument. The survey has a sensitivity some 3 times better than the standard HIJASS and HIPASS surveys. We detect 31 galaxies, 27 of which are well known cluster members. The four new detections have been confirmed in the HIPASS data and by follow up Jodrell Bank pointed observations. One object lies behind M86, but the other 3 have no obvious optical counter parts upon inspection of the digital sky survey fields. These 3 objects were mapped at Arecibo with a smaller \am{3}{6} HPBW and a 4 times better sensitivity than the Jodrell Bank data, which allow an improved determination of the dimensions and location of two of the objects, but surprisingly failed to detect the third. The two objects are resolved by the Arecibo beam giving them a size far larger than any optical images in the nearby field. To our mass limit of $5 \times 10^{7}$ $\frac{Δv}{50 km s^{-1}}$ $M_{\odot}$ and column density limit of $3 \times 10^{18}$ $\frac{Δv}{50 km s^{-1}}$ atoms cm$^{-2}$ these new detections represent only about 2% of the cluster atomic hydrogen mass. Our observations indicate that the \HI mass function of the cluster turns down at the low mass end making it very different to the field galaxy \HI mass function. This is quite different to the Virgo cluster optical luminosity function which is much steeper than that in the general field. Many of the sample galaxies are relatively gas poor compared to \HI selected samples of field galaxies, confirming the 'anaemic spirals' view of Virgo cluster late type galaxies.

astro-ph↗

arXiv2003

The dwarf Low Surface Brightness galaxy population of the Virgo Cluster I. The faint-end-slope of the Luminosity Function

The widely varying dwarf galaxy counts in different environments provide a strong challenge to standard hierarchical clustering models. The luminosity function is not universal, but seems to be strongly dependent upon environment. In this paper we describe an automated procedure for detecting and measuring very low surface brightness (LSB) features in deep CCD data. We apply this procedure to large area CCD survey fields of the Virgo cluster. We show that there are many more faint ($-10 \geq M_{B} \geq -14$) low surface brightness galaxies than what would be predicted from extrapolation of the Virgo cluster catalogue luminosity function. Over our limited range of measurement the faint end slope of the luminosity function becomes $α=- 1.6$. The luminosity function is flatter in the inner regions of the cluster than it is in the outer regions. Although these galaxies contribute a small fraction of the total stellar light of the cluster, they may contribute significantly to the mass in galaxies if they have large mass-to-light ratios similar to those recently measured for Local Group dwarf galaxies.

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