arXiv subjects

I. Aretxaga

Publications and source records attributed to I. Aretxaga.

At least 91 records · Page 5Linked to original sources

arXiv2008

The SCUBA Half-Degree Extragalactic Survey (SHADES) - VIII. The Nature of Faint Submm Galaxies in SHADES, SWIRE and SXDF Surveys

We present the optical-to-submm spectral energy distributions for 33 radio & mid-IR identified submillimetre galaxies discovered via the SHADES 850 micron SCUBA imaging in the Subaru-XMM Deep Field (SXDF). Optical data for the sources comes from the Subaru-XMM Deep Field (SXDF) and mid- and far-IR fluxes from SWIRE. We obtain photometric redshift estimates for our sources using optical and IRAC 3.6 and 4.5 micron fluxes. We then fit spectral energy distribution (SED) templates to the longer wavelength data to determine the nature of the far-IR emission that dominates the bolometric luminosity of these sources. The infrared template fits are also used to resolve ambiguous identifications and cases of redshift aliasing. The redshift distribution obtained broadly matches previous results for submm sources and on the SHADES SXDF field. Our template fitting finds that AGN, present in about 10% of sources, do not contribute significantly to their bolometric luminosity. Dust heating by starbursts, with either Arp220 or M82 type SEDs, appears to be responsible for the luminosity in most sources (23/33 are fitted by Arp220 templates, 2/33 by the warmer M82 templates). 8/33 sources, in contrast, are fit by a cooler cirrus dust template, suggesting that cold dust has a role in some of these highly luminous objects. Three of our sources appear to have multiple identifications or components at the same redshift, but we find no statistical evidence that close associations are common among our SHADES sources. Examination of rest-frame K -band luminosity suggests that 'downsizing' is underway in the submm galaxy population, with lower redshift systems lying in lower mass host galaxies. Of our 33 identifications six are found to be of lower reliability but their exclusion would not significantly alter our conclusions.

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arXiv2008

The SCUBA HAlf Degree Extragalactic Survey (SHADES) - VII. Optical/IR photometry and stellar masses of sub-millimeter galaxies

We present estimates of the photometric redshifts, stellar masses and star formation histories of sources in the SCUBA HAlf Degree Extragalactic Survey (SHADES). This paper describes the 60 SCUBA sources detected in the Lockman Hole covering an area of ~320 square arcmin. Using photometry spanning the B band to 8um, we find that the average SCUBA source forms a significant fraction of its stars in an early period of star formation and that most of the remainder forms in a shorter more intense burst around the redshift it is observed. This trend does not vary significantly with source redshift but the exact ratio of early to late mass is quite sensitive to the way extinction is treated in the modelling. However, the sources show a clear increase in stellar mass with redshift, consistent with downsizing. In terms of SED types, only two out of the 51 sources we have obtained photometric redshifts for are best fit by a quasar-like spectral energy distribution, with approximately 80 per cent of the sources being best fit with late-type spectra (Sc, Im and starburst). By including photometry at 850um, we conclude that the average SCUBA source is forming stars at a rate somewhere between 6 and 30 times the rate implied from the rest-frame optical in a dust obscured burst and that this burst creates 15-65 per cent of the total stellar mass. Using a simplistic calculation, we estimate from the average star formation history that between one in five and one in 15 bright (L_* +2 mag < L_optical < L_* -1 mag) galaxies in the field over the interval 0 < z < 3 will at some point in their lifetime experience a similar energetic dusty burst of star formation. Finally, we compute the evolution of the star formation rate density and find it peaks around z=2.

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arXiv2008

AzTEC Millimetre Survey of the COSMOS Field: I. Data Reduction and Source Catalogue

We present a 1.1 mm wavelength imaging survey covering 0.3 sq. deg. in the COSMOS field. These data, obtained with the AzTEC continuum camera on the James Clerk Maxwell Telescope (JCMT), were centred on a prominent large-scale structure over-density which includes a rich X-ray cluster at z = 0.73. A total of 50 millimetre galaxy candidates, with a significance ranging from 3.5-8.5 sigma, are extracted from the central 0.15 sq. deg. area which has a uniform sensitivity of 1.3 mJy/beam. Sixteen sources are detected with S/N > 4.5, where the expected false-detection rate is zero, of which a surprisingly large number (9) have intrinsic (de-boosted) fluxes > 5 mJy at 1.1 mm. Assuming the emission is dominated by radiation from dust, heated by a massive population of young, optically-obscured stars, then these bright AzTEC sources have FIR luminosities > 6 x 10^12 L(sun) and star formation-rates > 1100 M(sun)/yr. Two of these nine bright AzTEC sources are found towards the extreme peripheral region of the X-ray cluster, whilst the remainder are distributed across the larger-scale over-density. We describe the AzTEC data reduction pipeline, the source-extraction algorithm, and the characterisation of the source catalogue, including the completeness, flux de-boosting correction, false-detection rate and the source positional uncertainty, through an extensive set of Monte-Carlo simulations. We conclude with a preliminary comparison, via a stacked analysis, of the overlapping MIPS 24 micron data and radio data with this AzTEC map of the COSMOS field.

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arXiv2007

The SCUBA HAlf Degree Extragalactic Survey (SHADES) -- V. Submillimetre properties of near-infrared--selected galaxies in the Subaru/XMM--Newton deep field

We have studied the submillimetre (submm) properties of the following classes of near-infrared (NIR)-selected massive galaxies at high redshifts: BzK-selected star-forming galaxies (BzKs); distant red galaxies (DRGs); and extremely red objects (EROs). We used the SCUBA HAlf Degree Extragalactic Survey (SHADES), the largest uniform submm survey to date. Partial overlap of SIRIUS/NIR images and SHADES in SXDF has allowed us to identify 4 submm-bright NIR-selected galaxies, which are detected in the mid-infrared, 24 micron, and the radio, 1.4 GHz. We find that all of our submm-bright NIR-selected galaxies satisfy the BzK selection criteria, except for one galaxy whose B-z and z-K colours are however close to the BzK colour boundary. Two of the submm-bright NIR-selected galaxies satisfy all of the selection criteria we considered, i.e. they belong to the BzK-DRG-ERO overlapping population, or `extremely red' BzKs. Although these extremely red BzKs are rare (0.25 arcmin^{-2}), up to 20 % of this population could be submm galaxies. This fraction is significantly higher than that found for other galaxy populations studied here. Via a stacking analysis, we have detected the 850 micron flux of submm-faint BzKs and EROs in our SCUBA maps. While the contribution of z~2 BzKs to the submm background is about 10--15 % and similar to that from EROs typically at z~1, BzKs have a higher fraction (~30 %) of submm flux in resolved sources compared with EROs and submm sources as a whole. From the SED fitting analysis for both submm-bright and submm-faint BzKs, we found no clear signature that submm-bright BzKs are experiencing a specifically luminous evolutionary phase, compared with submm-faint BzKs. An alternative explanation might be that submm-bright BzKs are more massive than submm-faint ones.

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arXiv2007

The SCUBA HAlf Degree Extragalactic Survey (SHADES) - III. Identification of radio and mid-infrared counterparts to submillimetre galaxies

Determining an accurate position for a submm galaxy (SMG) is the crucial step that enables us to move from the basic properties of an SMG sample - source counts and 2-D clustering - to an assessment of their detailed, multi-wavelength properties, their contribution to the history of cosmic star formation and their links with present-day galaxy populations. In this paper, we identify robust radio and/or IR counterparts, and hence accurate positions, for over two thirds of the SCUBA HAlf-Degree Extragalactic Survey (SHADES) Source Catalogue, presenting optical, 24-um and radio images of each SMG. Observed trends in identification rate have given no strong rationale for pruning the sample. Uncertainties in submm position are found to be consistent with theoretical expectations, with no evidence for significant additional sources of error. Employing the submm/radio redshift indicator, via a parameterisation appropriate for radio-identified SMGs with spectroscopic redshifts, yields a median redshift of 2.8 for the radio-identified subset of SHADES, somewhat higher than the median spectroscopic redshift. We present a diagnostic colour-colour plot, exploiting Spitzer photometry, in which we identify regions commensurate with SMGs at very high redshift. Finally, we find that significantly more SMGs have multiple robust counterparts than would be expected by chance, indicative of physical associations. These multiple systems are most common amongst the brightest SMGs and are typically separated by 2-6", or 15-50/(sin i) kpc at z ~ 2, consistent with early bursts seen in merger simulations.

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arXiv2006

A broadband spectroscopic search for CO line emission in HDF850.1: the brightest submillimetre object in the Hubble Deep Field North

Using the 100-m Green Bank Telescope, we have conducted a cm-wavelength search for CO J=1-0 line emission towards the high-redshift, far-infrared luminous object, HDF850.1 over the redshift interval 3.3 nu(obs)>18.0 GHz), making HDF850.1 a potential occupent of the `high-redshift tail' of submm selected galaxies. We have also conducted a search for CO J=2-1 line emission over the narrower redshift range, 3.9<z<4.3. although we do not detect any CO line emission in this object, our limits to the CO line luminosity are in broad agreement with the median value measured in the current sample of high-redshift, submm selected objects detected in high-J CO line emission, but not sufficient to fully test the validity of the photometric redshift technique.

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arXiv2006

The SCUBA HAlf Degree Extragalactic Survey (SHADES) -- II. Submillimetre maps, catalogue and number counts

We present the maps, source catalogue and number counts of the largest, most complete and unbiased extragalactic submillimetre survey ever undertaken: the 850-micron SCUBA HAlf Degree Extragalactic Survey (SHADES). Using the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT), SHADES mapped two separate regions of sky: the Subaru/XMM-Newton Deep Field (SXDF) and the Lockman Hole East (LH). These SCUBA maps cover 720 square arcmin with an RMS noise level of about 2 mJy and have uncovered >100 submillimetre galaxies. In order to ensure the utmost robustness of the resulting source catalogue, data reduction was independently carried out by four sub-groups drawn within the SHADES team, providing an unprecedented degree of reliability with respect to other SCUBA catalogues available from the literature. Individual source lists from the four groups were combined to produce a robust 120-object SHADES catalogue; an invaluable resource for follow-up campaigns aiming to study the properties of a complete and consistent sample of submillimetre galaxies. We present differential and integral source number counts of submillimetre galaxies and find that the differential counts are better fit with a broken power-law or a Schechter function than with a single power-law; the SHADES data alone significantly show that a break is required at several mJy, although the precise position of the break is not well constrained. We also find that an 850-micron survey complete down to 2 mJy would resolve 20-30 per cent of the Far-IR background into point sources. [abridged]

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arXiv2005

Spectroscopic and Photometric Observations of SN IIn 1995N

We present the results of a long-term program of monitoring of the famous SN 1995N, observed both in photometry (UBVRIJHK bands) and optical spectroscopy. The observations span a period of about 9 years. These new data, together with others available in literature, extend from the X-ray wavelengths to the radio, and allow to estimate the total energy radiated by the supernova over a decade after its explosion.

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arXiv2004

Confirmation of the effectiveness of sub-mm source redshift estimation based on rest-frame radio to FIR photometry

We present a comparison between the published optical, IR and CO spectroscopic redshifts of 15 (sub-)mm galaxies and their photometric redshifts as derived from long-wavelength (radio-mm-FIR) photometric data. The redshift accuracy measured for 12 sub-mm galaxies with at least one robustly-determined colour in the radio-mm-FIR regime is dz=0.30 (r.m.s.). Despite the wide range of spectral energy distributions in the local galaxies that are used in an un-biased manner as templates, this analysis demonstrates that photometric redshifts can be efficiently derived for sub-mm galaxies with a precision of dz < 0.5 using only the rest-frame FIR to radio wavelength data.

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arXiv2003

Line Formation in the Inner Starburst Regions of AGN

We review the evidence for young stellar populations in the inner (< 200 pc) regions of Active Galactic Nuclei (AGN), and the physical mechanisms through which the stars can potentially create the emission lines that characterize AGN.

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arXiv2003

Breaking the "Redshift Deadlock" -- II: The redshift distribution for the submillimetre population of galaxies

In this paper we apply our Monte-Carlo photometric-redshift technique, introduced in paper I (Hughes et al. 2002), to the multi-wavelength data available for 77 galaxies selected at 850um and 1.25mm. We calculate a probability distribution for the redshift of each galaxy, which includes a detailed treatment of the observational errors and uncertainties in the evolutionary model. The cumulative redshift distribution of the submillimetre galaxy population that we present in this paper, based on 50 galaxies found in wide-area SCUBA surveys, is asymmetric, and broader than those published elsewhere, with a significant high-z tail for some of the evolutionary models considered. Approximately 40 to 90 per cent of the sub-mm population is expected to have redshifts in the interval 2 < z < 4. Whilst this result is completely consistent with earlier estimates for the sub-mm galaxy population, we also show that the colours of many (< 50 per cent) individual sub-mm sources, detected only at 850um with non-detections at other wavelengths, are consistent with those of starburst galaxies that lie at extreme redshifts, z > 4. Spectroscopic confirmation of the redshifts, through the detection of rest-frame FIR--mm wavelength molecular transition-lines, will ultimately calibrate the accuracy of this technique. We use the redshift probability distribution of HDF850.1 to illustrate the ability of the method to guide the choice of possible frequency tunings on the broad-band spectroscopic receivers that equip the large aperture single-dish mm and cm-wavelength telescopes.

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arXiv2002

SN1999E: Another piece in the SN-GRB connection puzzle

Detailed optical and near-IR observations of SN 1999E have confirmed early suggestions that this supernova was indeed a twin of the peculiar type II SN 1997cy: it was exceptionally luminous and had evolved slowly, and the line profiles had narrow peaks and broad wings, indicating interaction with the circumstellar material. Nevertheless, the most intriguing characteristic was that, in analogy to SN 1997cy, it exploded at a position consistent in time and location with a BATSE event (GRB980910). The "a posteriori" probability that the only two SNe with such an optical appearance are associated with two different BATSE GRB is only 0.2%. This raises the possibility that some GRB are associated with H--rich SNe.

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arXiv2002

Discovery of the host galaxy of HDF850.1, the brightest sub-mm source in the Hubble Deep Field

Despite extensive observational efforts, the brightest sub--mm source in the Hubble Deep Field, HDF850.1, has failed to yield a convincing optical/infrared identification almost 4 years after its discovery. This failure is all the more notable given the availability of supporting multi-frequency data of unparalleled depth, and sub-arcsec positional accuracy for the sub-mm/mm source. Consequently, HDF850.1 has become a test case of the possibility that the most violently star-forming objects in the universe are too red and/or distant to be seen in the deepest optical images. Here we report the discovery of the host galaxy of HDF850.1. This object has been revealed by careful analysis of a new, deep K-prime image of the HDF obtained with the Subaru 8.2-m telescope. Its reality is confirmed by a similar analysis of the HST NICMOS F160W image of the same region. This object is extremely faint (K=23.5), clumpy (on sub-arcsec scales) and very red (I-K > 5.2; H-K = 1.4 +- 0.35). The likelihood that it is the correct identification is strongly reinforced by a reanalysis of the combined MERLIN+VLA 1.4-GHz map of the field which yields a new radio detection of HDF850.1 only 0.1 arcsec from the new near-ir counterpart, and with sufficient positional accuracy to exclude all previously considered alternative optical candidates. We have calculated new confidence limits on the estimated redshift of HDF850.1 and find z = 4.1 +- 0.5. We also calculate that the flux density of HDF850.1 has been boosted by a factor of ~3 through lensing by the intervening elliptical 3-586.0, consistent with predictions that a small but significant fraction of blank-field sub-mm sources are lensed by foreground galaxies. We discuss the wider implications of these results for the sub-mm population and cosmic star-formation history.

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arXiv2002

Breaking the Redshift Deadlock - I: Constraining the star formation history of galaxies with sub-millimetre photometric redshifts

Future extragalactic sub-millimetre and millimetre surveys have the potential to provide a sensitive census of the level of obscured star formation in galaxies at all redshifts. While in general there is good agreement between the source counts from existing SCUBA (850um) and MAMBO (1.25mm) surveys of different depths and areas, it remains difficult to determine the redshift distribution and bolometric luminosities of the sub-millimetre and millimetre galaxy population. This is principally due to the ambiguity in identifying an individual sub-millimetre source with its optical, IR or radio counterpart which, in turn, prevents a confident measurement of the spectroscopic redshift. Additionally, the lack of data measuring the rest-frame FIR spectral peak of the sub-millimetre galaxies gives rise to poor constraints on their rest-frame FIR luminosities and star formation rates. In this paper we describe Monte-Carlo simulations of ground-based, balloon-borne and satellite sub-millimetre surveys that demonstrate how the rest-frame FIR-sub-millimetre spectral energy distributions (250-850um) can be used to derive photometric redshifts with an r.m.s accuracy of +/- 0.4 over the range 0 < z < 6. This opportunity to break the redshift deadlock will provide an estimate of the global star formation history for luminous optically-obscured galaxies [L(FIR) > 3 x 10^12 Lsun] with an accuracy of 20 per cent.

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arXiv2002

Optical and infrared observations of the supernova SN 1999el

Optical and near-infrared light curves of the Type IIn supernova 1999el in NGC 6951 are presented. A period of 220 days (416 days in the near-infrared) is covered from the first observation obtained a few days before maximum light. Spectroscopic observations are also discussed. Using as a distance calibrator the Type Ia SN 2000E, which occurred some months later in the same galaxy, and fitting a blackbody law to the photometric data we obtain a maximum bolometric luminosity for SN 1999el of $\sim 10^{44}$ erg s$^{-1}$. In general, the photometric properties of SN 1999el are very similar to those of SN 1998S, a bright and well studied Type IIn SN, showing a fast decline in all observed bands similar to those of Type II-L SNe. The differences with SN 1998S are analyzed and ascribed to the differences in a pre-existing circumstellar envelope in which dust was already present at the moment of the SN outburst. We infer that light echoes may play a possibly significant role in affecting the observed properties of the light curves, although improved theoretical models are needed to account for the data. We conclude that mass loss in the progenitor RG stars is episodic and occurs in an asymmetric way. This implies that collapsing massive stars appear as normal Type II SN if this occurs far from major mass loss episodes, whereas they appear as Type IIn SNe if a large mass loss episode is in progress.

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arXiv1999

SN 1988Z: Spectro-photometric catalogue and energy estimates

We present a spectro-photometric catalogue of the evolution of supernova 1988Z which combines new and published observations in the radio, optical and X-ray bands, with the aim of offering a comprehensive view of the evolution of this object and deriving the total energy radiated since discovery. The major contribution to the total radiated energy comes at optical to X-ray frequencies, with a total emission of at least $2 \times 10^{51}$ erg (for Ho=50 km/s) in 8.5 years. A model-dependent extrapolation of this value indicates that the total radiated energy may be as high as $10^{52}$ erg. The high value of the radiated energy supports a scenario in which most of the kinetic energy of the ejecta is thermalized and radiated in a short interaction with a dense circumstellar medium of nearly constant density. In this sense, 1988Z is not a supernova but a young and compact supernova remnant.

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arXiv1999

When SN explode in a Starburst: Transitions among AGN types

Among the Active Galactic Nuclei (AGN) that have suffered type mutations, the classically classified Seyfert 2 NGC 7582 recently found at a Seyfert 1 stage, is perhaps one of the most puzzling cases, since it defies a well supported case for unification. We investigate the possibility that this type transition, common to other 12 AGN, is driven by supernovae (SN) exploding in a nuclear/circumnuclear starburst.

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arXiv1998

Adaptive Optics observations of LBQS 0108+0028: K-band detection of the host galaxy of a radio-quiet QSO at z=2

We report the first unambiguous detection of the host galaxy of a normal radio-quiet QSO at high-redshift in K-band. The luminosity of the host comprises about 35% of the total K-band luminosity. Assuming the average colour of QSOs at z=2, the host would be about 5 to 6 mag brighter than an unevolved L* galaxy placed at z=2, and 3 to 4 mag brighter than a passively evolved L* galaxy at the same redshift. The luminosity of the host galaxy of the QSO would thus overlap with the highest found in radio-loud QSOs and radio-galaxies at the same redshift.

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