Modelling ISO Galaxy Counts with Luminosity and Merger Rate Evolution

We model galaxy evolution in the 6.75 and 15 micron passbands of the ISO satellite, by combining models of galaxy evolution at optical wavelengths (which are consistent with the optical galaxy counts) with observed spectral energy distributions in the infra-red. Our model is consistent with the local 12 micron galaxy luminosity, if 3.5 per cent of spirals at z=0 are in interacting pairs with mid-infra-red luminosities enhanced by major starbursts. Source counts from deep ISO surveys exceed non-evolving predictions but are more consistent with our evolving model. The steep number count of 6.75 micron sources appears to be explained primarily by evolving early-type galaxies, whereas at 15 microns the main contributors are star-forming spirals and starbursting interacting/merging galaxies. The 31 per cent of 15 micron sources which are visibly interacting galaxies have high mid-infra-red/optical flux ratios indicating major starbursts combined with dust extinction. The numbers and high mean redshift of these sources suggest the merger-starbursts are increasing in luminosity with redshift, approximately as (1+z)^2, in addition to undergoing (1+z)^2 number evolution reflecting the optically observed increase with redshift in the fraction of interacting galaxies.Comment: 12 pages, Latex, 12 figures, submitted to MNRA

Lyman-alpha Imaging of a Very Luminous z=2.3 Starburst Galaxy with WFPC2

We investigate a very luminous Lyman-alpha emitting galaxy, associated with a z=2.3 damped absorption system in the spectrum of the QSO PHL 957. The galaxy was observed with the HST WFPC2, through a narrow filter (F410M) corresponding to rest-frame Lyman -alpha, for 41.2 ksec, with shorter exposures in F555W and F814W. The galaxy is resolved into a close (0.35 arcsec) pair of two components, CFgA and CFgB. The profile of CFgA is consistent with an exponential disk, but CFgB is closer to a bulge galaxy. Fr om the observed colours we estimate rest-frame Lyman-alpha equivalent widths of 151 Angstroms for CFgA and 33 for CFgB. From the F814W and F555W magnitudes we estimate rest-frame blue-band absolute magnitudes of -23.12 for CFgA and -23.24 for CFgB, signi ficantly brighter than local galaxies of the same size. CFgA shows a remarkable 3.9 magnitudes of surface brightness enhancement relative to local spirals, and we speculate that this may be the result of a very luminous starburst, triggered by the merger of the two components. The Lyman-alpha emission could be from a brief phase early in the starburst in which most of these photons can escape. We search for other z=2.3 galaxies with strong Lyman-alpha emission, selecting these by a colour F410M-F555W<-0.2. Eight candidate sources, all fainter than CFgA, are identified. One is a point-source and may be an AGN; the others are irregular a nd of low surface brightness, appearing typical of Lyman break galaxies, but with Lyman-alpha equivalent widths near 100 Angstroms.Comment: 17 pages, Latex, 17 figures. Accepted for publication in MNRA

The Clustering of K\sim 20 Galaxies on 17 Radio Galaxy Fields

We investigate the angular correlation function, $\omega(\theta)$, of the galaxi es detected in the K-band on 17 fields (101.5 square arcmin in total), each containing a $z\sim 1.1$ radio galaxy. There is a significant detection of galaxy clustering at $K\sim 20$ limits, with an amplitude higher than expected from simple models which fit the faint galaxy clustering in the blue and red passbands, but consistent with a pure luminosity evolution model i f clustering is stable and early-type galaxies have a steeper correlation function than spirals. We do not detect a significant cross-correlation between the radio galaxies and the other galaxies on these fields, obtaining upper limits consistent with a mean clustering environment of Abell class 0 for $z\sim 1.1$ radio galaxies, similar to that observed for radio galaxies at $z\sim 0.5$. At $K\leq 20$, the number of galaxy-galaxy pairs of 2--3 arcsec separations exceeds the random expectation by a factor of $2.15\pm 0.26$. This excess suggests at least a tripling of the local merger rate at $z\sim 1$.Comment: 13 pages, 3 tables, 7 postscript figures, TEX, submitted to MNRA

The Morphology of 9 Radio-selected Faint Galaxies from deep HST Imaging

Using the HST WFPC2 we perform deep I-band imaging of 9 radio-selected (limit 14 microJanskys at 8.5 GHz) faint galaxies from Roche, Lowenthal and Koo (2002). Two are also observed in V. Six of the galaxies have known redshifs of 0.4<z<1.0. Radial intensity profiles indicate that 7 are disk galaxies and 2 are bulge-dominated. Four of the six with redshifts have a high optical surface brightness compared to typical disk galaxies. Two of the 9 galaxies are in close interacting pairs, another two are very asymmetric and three have large, luminous rings resembling the collisional starburst rings in the Cartwheel galaxy. In most of these galaxies the high radio luminosities are probably the result of interaction-triggered starbursts. The mixture of observed morphologies suggests that enhanced radio luminosities often persist for >0.2 Gyr, to a late stage of the interaction. One of these 9 galaxies may be an exception in that it is a large red elliptical and its strong radio emission is more likely to be from an obscured AGN.Comment: 12 pages, latex, 8 figures, accepted for publication in MNRA

Morphology and Surface Brightness Evolution of z\sim1.1 Radio Galaxies

We use $K-band imaging to investigate the angular size and morphology of 10 6C radio galaxies, at redshifts$1\leq z\leq 1.4$. Two appear to be undergoing mergers, another contains two intensity peaks aligned with the radio jets, while the other seven appear consistent with being normal ellipticals in the K-band. Intrinsic half-light radii are estimated from the areas of each radio galaxy image above a series of thresholds. The 6C galaxy radii are found to be significantly smaller than those of the more radioluminous 3CR galaxies at similar redshifts. This would indicate that the higher mean K-band luminosity of the 3CR galaxies results from a difference in the size of the host galaxies, and not solely from a difference in the power of the active nuclei. The size-luminosity relation of the$z\sim 1.1$6C galaxies indicates a 1.0--1.8 mag enhancement of the rest-frame R-band surface brightness relative to either local ellipticals of the same size or FRII radio galaxies at$z<0.2$. The 3CR galaxies at$z\sim 1.1$show a comparable enhancement in surface brightness. The mean radius of the 6C galaxies suggests that they evolve into ellipticals of$L\sim L^*$luminosity, and is consistent with their low redshift counterparts being relatively small FRII galaxies, a factor$\sim 25$lower in radio luminosity, or small FRI galaxies a factor of$\sim 1000$ lower in radio luminosity. Hence the 6C radio galaxies may undergo at least as much optical and radio evolution as the 3CR galaxies.Comment: 17 pages, 7 postscript figures, TEX, submitted to MNRA

The clustering and X-ray properties of faint galaxies

The clustering properties of faint (23 ≤ B ≤ 27) galaxies were investigated, with the aim of obtaining information about their redshift distribution, N(z), and therefore about the processes of galaxy evolution causing the steep rise in the galaxy number counts at B > 23. We calculated the angular correlation function, w(θ), for galaxies detected on a CCD survey reaching a blue magnitude of B(_eed) = 25.0 and a red magnitude of R(_eed) = 23.5, and on a smaller area reaching a very faint limit of B(_eed) = 27.0. The w(θ) amplitude of galaxies was found to decrease much more steeply between magnitude limits of B(_eed) = 23 and B(_eed) = 25 than predicted by models in which galaxy clustering is stable in proper co-ordinates and the galaxy redshift distribution possesses a no-evolution form. At a B = 24.5 limit the w(θ) amplitude was found to be only ~ (^1)(_4) that expected from a non-evolving model, enabling us to reject such a model at the 4σ level. The red-limited sample, R(_eed) = 23.5, also gave a w(θ) amplitude lower than the non-evolving prediction, although the difference was less significant (~ 2σ). A pure luminosity evolution model, which accounts for the excess in the galaxy number counts by enabling galaxies undergoing rapid star-formation at 1 ≤ z ≤ 4 to become visible at B > 23.5, gave a good fit to the w (θ) results without requiring any departure from stable clustering. The B(_eed) ≤ 24.5 galaxies with redder (B - R ≥ 1.5) colours gave a significantly higher w(θ) amplitude than the bluer galaxies at the same limit, consistent with a stable clustering model with no luminosity evolution. As these red galaxies would lie at z 23.5 as being caused by the appearance of blue star-forming galaxies at high redshifts. If all the blue galaxies seen at B ~ 24.5 are instead at z 24.5 than the predictions of q(_0) = 0.5 PLE models, and appear to rise more steeply at 25 ≤ B ≤ 27.5, with (^d(logN))(_dm) ~ 0.3, than even our q(_0) = 0.05 PLE model would predict. The observed number count gradient at B > 25, in combination with the levelling out of the w(θ) scaling, would then suggest that the luminosity function steepens to a ~ -1.75 at high redshifts, in addition to undergoing the strong brightening of the L* luminosity predicted by PLE models. We also investigated the X-ray properties of faint (18 ≤ B ≤ 23) galaxies, by cross- correlating their positions with those of X-ray sources (without identifications as either QSOs or stars) detected on deep ROSAT images. The results indicated that ~ 1% of all B ≤ 21 galaxies were detected above a 4σ threshold on the ROSAT X-ray images, with the cross-correlation between sources and galaxies being of 3σ significance. As the detected galaxies would possess L(_X)/L(_B) ratios higher than those typical of local galaxies by factors of ~ 100, these results suggest a wide dispersion of σ ~ 0.8 in the distribution of log (L(_X)/L(_B)) for galaxies. Spectroscopic investigation of the galaxies identified as probable X-ray sources indicated that they included both star-forming and early-type galaxies, with a mean redshift of z ~ 0.22, and were mainly of L ~ L* luminosity in the blue band, but possessed very high X-ray luminosities of L(_X) ~ 10(^42) ergs s(^-1) On one ROSAT image we also detected a rich galaxy cluster at a high redshift of z = 0.561, and estimated its X-ray luminosity as L(_X) - 5.4 X 10(^43) ergs s(^-1), which is only about ~ 30% of that expected for a cluster of the same richness seen locally. The number counts of galaxies in the 0.5-2.0 keV band were estimated as 27.18 ± 10.35 deg(^-2) at a flux limit of 10(^-14.4) ergs cm(^-2)s(^-1) The number counts of detected QSOs appear to level out at ~ 10(^-14) ergs cm(^-2)s(^-1) suggesting that QSOs faintward of our detection limits would produce only ~ 30% of the unresolved X-ray background (XRB).The autocorrelation function (ACF) of the unresolved 0.5-2.0 keV XRB was measured on 3 ROSAT images (totalling 1.05 deg(^2)), and was found to show no significant signal - we obtained a 2σ upper limit of w(θ) ≤ 1.4 x 10(^-3)(deg)(^-0.8) on its amplitude. This would be consistent with normally clustered galaxies as the origin of most of the XRB, if their X-ray luminosity increases with redshift sufficiently that a large proportion of the X-ray flux is produced by galaxies at z > 1. A very significant (> 5σ) cross-correlation was detected between 18 ≤ B ≤ 23 galaxies on A AT photographic plates and the fluctuations in the unresolved XRB on the same 3 ROSAT images. The cross-correlation amplitude, after applying corrections for the effects of galaxy clustering, indicated that these 18 ≤ B ≤ 23 galaxies produced 16.8 ± 2.1% of the unresolved 0.5-2.0 keV background, corresponding to a volume X-ray emissivity of p(0.5-2.0 keV) = (5.27 ± 0.65) x l0(^38) ergs s(^-1)Mpc(^-3). This is about an order of magnitude higher than the emissivity expected from the L(_X)/L(_B) ratio typical of normal galaxies, but a σ ~ 0.8 dispersion in log L(_X)/L(_B) ratios could account for this. The number counts of X-ray detected galaxies and the galaxy/XRB cross-correlation amplitude are both consistent with a slightly smaller dispersion in log (L(_X)/L(_B)) of σ = 0.7, if combined with an exponential increase with look-back time of the X-ray luminosity of galaxies, with a timescale of r = 0.4H(_o)(^-1). Extrapolation of our estimate of the galaxy X-ray emissivity to higher redshifts, predicts that non-evolving galaxies would account for ~ 35% of the unresolved 0.5-2.0 keV background, with most of the galaxy contribution produced at z < 1. However, with a r = 0.4H(_0)(^-1) rate of X-ray luminosity evolution, the predicted contribution of high-redshift (1 ≤ z ≤ 4) galaxies to the XRB is greatly increased, accounting for the lack of signal in the ACF. Galaxies out to z ~ 4 would then produce in total ~ 70% of the unresolved XRB, accounting for the entire non-QSO component. No part of this work has previously been submitted for a degree in any University. Some of the results described in this thesis have been published elsewhere in the following paper

Integral Field Spectroscopy of the cometary starburst galaxy NGC 4861

Financial support from the Spanish Ministerio de Economía y Competitividad under grant PID2019-107408GB-C44, from Junta de Andalucia under project P18-FR-2664, and also from the grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033. P P thanks Fundaçao para a Ciencia e a Tecnologia (FCT) for managing research funds graciously provided to Portugal by the EU. This work was supported through FCT grants UID/FIS/04434/2019, UIDB/04434/2020, UIDP/04434/2020 and the project ‘Identifying the Earliest Supermassive Black Holes with ALMA (IdEaS with ALMA) (PTDC/FIS-AST/29245/2017)’ SDP is grateful to the Fonds de Recherche du Québec - Nature et Technologies. SDP also acknowledges financial support from Juan de la Cierva Formación Fellowship (FJC2021-047523-I) financed by MCIN/AEI/10.130395011000110333 and by the European Union "NextGenerationEU"/PRTR. This study is based on observations collected at the Centro As- tronómico Hispano en Andalucía (CAHA) at Calar Alto, Spain, operated jointly by the Instituto de Astrofísica de Andalucía (CSIC) and Junta de Andalucía. The CAHA Archive is part of the Spanish Virtual Observatory project funded by MCIN/AEI/10.13039/501100011033 through grant PID2020-112949GB-I00 CAB (INTA-CSIC). Part based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Fa-cility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA). This research has made use of the NASA/IPAC Extragalactic Data base (NED), which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology.Using the PMAS Integral Field Unit on the Calar Alto 3.5 m telescope, we observed the southern component (Markarian 59) of the ‘cometary’ starburst galaxy NGC 4861. Mrk 59 is centred on a giant nebula and concentration of stars 1 kpc in diameter. Strong H α emission points to a star-formation rate (SFR) at least 0.47 M⊙ yr−1. Mrk 59 has a very high [O III] λ5007/H β ratio, reaching 7.35 in the central nebula, with a second peak at a star-forming hotspot further north. Fast outflows are not detected but nebular motion and galaxy rotation produce relative velocities up to 40 km s−1. Spectral analysis of different regions with ‘Fitting Analysis using Differential evolution Optimization’ (FADO) finds that the stars in the central and ‘spur’ nebulae are very young, ≤ 125 Myr with a large < 10 Myr contribution. Older stars (∼ 1 Gyr) make up the northern disk component, while the other regions show mixtures of 1 Gyr age with very young stars. This and the high specific SFR ∼ 3.5 Gyr−1 imply a bimodal star formation history, with Mrk 59 formed in ongoing starbursts fuelled by a huge gas inflow, turning the galaxy into an asymmetric ‘green pea’ or blue compact dwarf. We map the He II λ4686 emission, and identify a broad component from the central nebula, consistent with the emission of ∼300 Wolf–Rayet stars. About a third of the He II λ4686 flux is a narrow line emitted from a more extended area covering the central and spur nebulae, and may have a different origin.Centro Astronómico Hispano en AndalucíaIPACNational Aeronautics and Space Administration NASAEuropean Commission PTDC/FIS-AST/29245/2017, UID/FIS/04434/2019 ECEuropean Space Agency ESAMinisterio de Economía y Competitividad PID2019-107408GB-C44 MINECOMinisterio de Ciencia e Innovación MICINNJunta de Andalucía CEX2021-001131-S, P18-FR-2664Agencia Estatal de Investigación AEIInstituto de Astrofísica de Andalucía PID2020-112949GB-I00 CAB (INTA-CSIC IA