arXiv subjects

S. Madden

Publications and source records attributed to S. Madden.

99 records · Page 6Linked to original sources

arXiv2007

PAHs in the Halo of NGC 5529

We present sensitive ISO $λ6.7 μ$m observations of the edge-on galaxy, NGC 5529, finding an extensive MIR halo around NGC 5529. The emission is dominated by PAHs in this band. The PAH halo has an exponential scale height of 3.7 kpc but can still be detected as far as $\approx 10$ kpc from the plane to the limits of the high dynamic range (1770/1) data. This is the most extensive PAH halo yet detected in a normal galaxy. This halo shows substructure and the PAHs likely originate from some type of disk outflow. PAHs are long-lived in a halo environment and therefore continuous replenishment from the disk is not required (unless halo PAHs are also being destroyed or removed), consistent with the current low SFR of the galaxy. The PAHs correlate spatially with halo H$α$ emission, previously observed by Miller & Veilleux (2003); both components are likely excited/ionized by in-disk photons that are leaking into the halo. The presence of halo gas may be related to the environment of NGC 5529 which contains at least 17 galaxies in a small group of which NGC 5529 is the dominant member. Of these, we have identified two new companions from the SDSS.

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arXiv2006

Extragalactic Science with Herschel-SPIRE

SPIRE, the Spectral and Photometric Imaging Receiver, is one of three instruments to fly on ESA's Herschel Space Observatory. It contains a three-band imaging photometer operating at 250, 360 and 520 microns, and an imaging Fourier Transform Spectrometer (FTS) covering 200-670 microns. It will be used for many extragalactic science programmes, a number of which will be implemented as Herschel Key Projects. The SPIRE consortium's Guaranteed Time (GT) programme will devote more than 1000 hours to Key Projects covering the high-z universe and local galaxies. It is also expected that substantial amounts of Herschel Open Time will be used for further extragalactic investigations. The high-z part of the SPIRE GT programme will focus on blank-field surveys with a range of depths and areas optimised to sample the luminosity-redshift plane and characterise the bolometric luminosity density of the universe at high z. Fields will be selected that are well covered at other wavelengths to facilitate source identifications and enable detailed studies of the redshifts, spectral energy distributions, and infrared properties of detected galaxies. The local galaxies programme will include a detailed spectral and photometric study of a sample of well resolved nearby galaxies, a survey of more than 300 local galaxies designed to provide a statistical survey of dust in the nearby universe, and a study of the ISM in low-metallicity environments, bridging the gap between the local universe and primordial galaxies.

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arXiv2006

Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams

Color-magnitude diagrams (CMDs) are presented for the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the Large Magellanic Cloud (LMC). IRAC and MIPS 24 um epoch one data are presented. These data represent the deepest, widest mid-infrared CMDs of their kind ever produced in the LMC. Combined with the 2MASS survey, the diagrams are used to delineate the evolved stellar populations in the Large Magellanic Cloud as well as Galactic foreground and extragalactic background populations. Some 32000 evolved stars brighter than the tip of the red giant branch are identified. Of these, approximately 17500 are classified as oxygen-rich, 7000 carbon-rich, and another 1200 as ``extreme'' asymptotic giant branch (AGB) stars. Brighter members of the latter group have been called ``obscured'' AGB stars in the literature owing to their dusty circumstellar envelopes. A large number (1200) of luminous oxygen--rich AGB stars/M supergiants are also identified. Finally, there is strong evidence from the 24 um MIPS channel that previously unexplored, lower luminosity oxygen-rich AGB stars contribute significantly to the mass loss budget of the LMC (1200 such sources are identified).

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arXiv2002

Mid-infrared observations of the ultraluminous galaxies IRAS14348-1447, IRAS19254-7245, and IRAS23128-5919

We present a study of the three ultraluminous infrared galaxies IRAS14348-1447, IRAS19254-7245, and IRAS23128-5919, based on mid-infrared (MIR) spectro-imaging (5-18microns) observations performed with ISOCAM. We find that the MIR emission from each system, which consists of a pair of interacting late type galaxies, is principally confined to the nuclear regions with diameters of 1-2kpc and can account for more than 95% of their IRAS 12micron flux. In each interacting system, the galaxy hosting an active galactic nucleus (AGN) dominates the total spectrum and shows stronger dust continuum (12-16microns) relative to the Unidentified Infrared Band (UIB) emission (6-9microns), suggestive of its enhanced radiation field. The MIR dominant galaxy also exhibits elevated 15micron/Halpha and 15micron/K ratios which trace the high extinction due to the large quantities of molecular gas and dust present in its central regions. Using only diagnostics based on our mid-infrared spectra, we can establish that the Seyfert galaxy IRAS19254-7245 exhibits MIR spectral features of an AGN while the MIR spectrum of the Seyfert (or LINER) member of IRAS23128-5919 is characteristic of dust emission principally heated by star forming regions.

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arXiv2001

The impact of bars on the mid-infrared dust emission of spiral galaxies: global and circumnuclear properties

We study the mid-infrared properties of a sample of 69 nearby spiral galaxies, selected to avoid Seyfert activity contributing a significant fraction of the central energetics, or strong tidal interaction, and to have normal infrared luminosities. These observations were obtained with ISOCAM, which provides an angular resolution of the order of 10 arcsec (half-power diameter of the point spread function) and low-resolution spectro-imaging information. Between 5 and 18 microns, we mainly observe two dust phases, aromatic infrared bands and very small grains, both out of thermal equilibrium. On this sample, we show that the global F15/F7 colors of galaxies are very uniform, the only increase being found in early-type strongly barred galaxies, consistent with previous IRAS studies. The F15/F7 excesses are unambiguously due to galactic central regions where bar-induced starbursts occur. However, the existence of strongly barred early-type galaxies with normal circumnuclear colors indicates that the relationship between a distortion of the gravitational potential and a central starburst is not straightforward. As the physical processes at work in central regions are in principle identical in barred and unbarred galaxies, and since this is where the mid-infrared activity is mainly located, we investigate the mid-infrared circumnuclear properties of all the galaxies in our sample. We show how surface brightnesses and colors are related to both the available molecular gas content and the mean age of stellar populations contributing to dust heating. Therefore, the star formation history in galactic central regions can be constrained by their position in a color-surface brightness mid-infrared diagram.

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arXiv2001

The first ISO ERO: a dusty quasar at z = 1.5

We report the discovery of an extremely red object (ERO) in a medium-deep ISOCAM extragalactic survey. The object is also a radio source. Subsequent VLT NIR spectroscopy revealed a prominent Halpha line giving a redshift of 1.5. We present the spectrum and photometric data points and discuss evidence that ISO J1324-2016 is a quasar harbouring a significant amount of very hot dust.

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arXiv2001

An atlas of mid-infrared dust emission in spiral galaxies

We present maps of dust emission at 7 microns and 15 microns/7 microns intensity ratios of selected regions in 43 spiral galaxies observed with ISOCAM. This atlas is a complement to studies based on these observations, dealing with star formation in centers of barred galaxies and in spiral disks. It is accompanied by a detailed description of data reduction and an inventory of generic morphological properties in groups defined according to bar strength and HI gas content.

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arXiv1998

Dust in an extremely metal-poor galaxy: mid-infrared observations of SBS 0335-052

The metal deficient (Z = Z_sun/41) Blue Compact Dwarf Galaxy (BCD) SBS 0335-052 was observed with ISOCAM between 5 and 17 mic. With a L_12mic/L_B ratio of 2.15, the galaxy is unexpectedly bright in the mid-infrared for such a low-metallicity object. The mid-infrared spectrum shows no sign of the Unidentified Infrared Bands, which we interpret as an effect of the destruction of their carriers by the very high UV energy density in SBS 0335-052. The spectral energy distribution (SED) is dominated by a very strong continuum which makes the ionic lines of [SIV] and [NeIII] very weak. From 5 to 17 mic, the SED can be fitted with a grey-body spectrum, modified by an extinction law similar to that observed toward the Galactic Center, with an optical depth of A_V~19-21 mag. Such a large optical depth implies that a large fraction (as much as ~ 75%) of the current star-formation activity in SBS 0335-052 is hidden by dust with a mass between 3x10^3 M_sun and 5x10^5 M_sun. Silicate grains are present as silicate extinction bands at 9.7 and 18 mic can account for the unusual shape of the MIR spectrum of SBS 0335-052. It is remarkable that such a nearly primordial environment contains as much dust as galaxies which are 10 times more metal-rich. If the hidden star formation in SBS 0335-052 is typical of young galaxies at high redshifts, then the cosmic star formation rate derived from UV/optical fluxes would be underestimated.

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arXiv1998

Mid--IR emission of galaxies in the Virgo cluster: II. Integrated properties

We analyse the integrated properties of the Mid-IR emission of a complete, optically selected sample of galaxies in the Virgo cluster observed with the ISOCAM instrument on board the ISO satellite. The analysis shows that the Mid-IR emission up to 15 mic of optically-selected, normal early-type galaxies (E, S0 and S0a) is dominated by the Rayleigh-Jeans tail of the cold stellar component. The Mid-IR emission of late-type galaxies is instead dominated by the thermal emission from dust. The small dust grains emitting in the Mid-IR have an excess of emission if compared to big grains emitting in the Far-IR. While the Far-IR emission increases with the intensity of the interstellar radiation field, their Mid-IR emission is non--linearly related to the UV radiation field. The spectral energy distributions of the target galaxies indicate that there is a linear relationship between the UV radiation field and the Mid-IR emission of galaxies for low or intermediate activities of star formation, while the emission from the hot dust seems to drop for strong UV fields. The Mid-IR colour of late-type galaxies is not related to their activity of star formation. The properties of the dust emission in the Mid-IR seem more related to the mass than to the morphological type of the target galaxy. Since the activity of star formation is anticorrelated to the mass of galaxies, this reflects a relationship between the emission of dust in the Mid-IR and the UV radiation field: galaxies with the lowest Mid-IR emission for a given UV field are low mass, dwarf galaxies. These observational evidences are easily explained if the carriers of the Unidentified Infrared Bands that dominate the 6.75 mic emission are destroyed by the intense UV radiation field of dwarf galaxies, although abundance effects can also play a role.

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