arXiv subjects

Neil Trentham

Publications and source records attributed to Neil Trentham.

49 records · Page 3Linked to original sources

arXiv1998

Ultraluminous infrared galaxies at high redshift: their position on the Madau plot and their fate

A major recent development in extragalactic astronomy has been the discovery of a population of galaxies that are luminous at submillimetre wavelengths. Estimates of their spectral energy distributions suggest that these galaxies are the high-redshift analogues of the ultraluminous infrared galaxies (ULIGs) observed locally. We identify plausible (but non-unique) redshift-dependent galaxy luminosity functions that are consistent with both source counts at 2800, 850, 450 and and 175 microns, and far-infrared background radiation intensities at 850, 240 and 140 microns. In all our models, most of the submillimetre-luminous sources are distant galaxies with high bolometric luminosities >= 10^12 L_sun. As for many local ULIGs it is not possible to determine whether these luminous galaxies are powered by starbursts, like the local galaxy Arp 220, or by active galactic nuclei (AGN), like the local galaxy Markarian 231. If the submillimetre-luminous galaxies are all starbursts, then we predict that the fraction of the cosmic star-formation rate in these objects is large, but but does not necessarily dominate the star-formation rate of the Universe at any redshift. Only a few per cent by mass of the present-epoch spheroidal stellar population would have been formed in such a population of star-forming galaxies, consistent with constraints on the number of galaxies with old stellar populations in the field at low and intermediate redshift derived from K-band surves. If the submillimetre-luminous galaxies are all powered by AGN, then the comoving density of supermassive black holes onto which material is accreting at high redshift probably equals no more than a few per cent of the local density of massive dark objects.

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arXiv1998

Starburst-driven Starbursts in the Heart of Ultraluminous Infrared Galaxies

There is increasing evidence for the presence of blue super star clusters in the central regions of ultraluminous infrared galaxies like Arp 220. Ultraluminous galaxies are thought to be triggered by galaxy mergers, and it has often been argued that these super star clusters may form during violent collisions between gas clouds in the final phase of the mergers. We now investigate another set of models which differ from previous ones in that the formation of the super star clusters is linked directly to the very intense starburst occurring at the very center of the galaxy. Firstly we show that a scenario in which the super star clusters form in material compressed by shock waves originating from the central starburst is implausible because the objects so produced are much smaller than the observed star clusters in Arp 220. We then investigate a scenario (based on the Shlosman-Noguchi model) in which the infalling dense gas disk is unstable gravitationally and collapses to form massive gaseous clumps. Since these clumps are exposed to the external high pressure driven by the superwind (a blast wave driven by a collective effect of a large number of supernovae in the very core of the galaxy), they can collapse and then massive star formation may be induced in them. The objects produced in this kind of collapse have properties consistent with those of the observed super star clusters in the center of Arp 220.

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arXiv1998

Evolution of the near-infrared luminosity function in rich galaxy clusters

We present the K-band (2.2 microns) luminosity functions of the X-ray luminous clusters MS1054-0321 (z=0.82), MS0451-0305 (z=0.55), Abell 963 (z=0.206), Abell 665 (z=0.182) and Abell 1795 (z=0.063) down to absolute magnitudes M_K = -20. Our measurements probe fainte absolute magnitudes than do any previous studies of the near-infrared luminosity function of clusters. All clusters are found to have similar luminosity functions within the errors, when the galaxy populations are evolved to redshift $z=0$. It iw known that the most massive bound systems in the Universe at all redshifts are X-ray luminous clusters. Therefore, assuming that the clusters in our sample correspond to a single population seen at different redshifts, the results here imply that not only had the stars in present-day ellipticals in rich clusters formed by z=0.8, but that they existed in as luminous galaxies then as they do today. Additionally, the clusters have K-band luminosity functions which appear to be consistent with the Kband field luminosity function in the range -24 < M_K < -22, although the uncertainties in both the field and cluster samples are large.

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arXiv1998

The faint end of the luminosity function in clusters

I review recent measurements of the faint end of the galaxy luminosity function in galaxy clusters. Evidence is presented that the luminosity function of galaxies in the central parts of clusters is remarkably constant between clusters and that this luminosity function is steep at bright and faint magnitudes and shallow in-between. The curvature is highly significant -- neither a power-law nor a Schechter function is consistent with the data. At no magnitude does alpha=-1 fit the data well. The faintest galaxies in all clusters that have been studied are dwarf spheroidal galaxies.

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arXiv1997

The discovery of a giant debris arc in the Coma Cluster

We present the discovery a giant low surface-brightness arc, of length luminous matrix with surface-brightness mu_B < 26.5 mag arcsec^{-2} and a number of embedded condensations. It is not associated with any giant galaxy in Coma in particular; neither does it have the properties of a gravitational arc. We argue that a fast interaction between the nearby barred S0 galaxy IC 4026 and either IC 4041 or RB 110 is the most natural explanation for the origin of the arc.

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arXiv1997

Near-infrared luminosity function and colours of dwarf galaxies in the Coma Cluster

We present K-band observations of the low-luminosity galaxies in the Coma cluster, which are responsible for the steep upturn in the optical luminosity function at M_R ~ -16, discovered recently. The main results of this study are (i) The optical$-$near-infrared colours of these galaxies imply that they are dwarf spheroidals. The median M-K colour for galaxies with -19.3 < M_K < -16.3 is 3.6 mag. (ii) The K-band luminosity function in the Coma cluster at the faint-end is not wee constrained, because of the uncertainties due to the field-to-field variance of the background. However, within the estimate large errors, it is consistent with the R-band luminosity function, shifted by $\sim3$ magnitudes. (iii) Many of the cluster dwarfs lie in a region of the B-K vs. B-R colour-colour diagram where background galaxies are rare Local dwarf spheroidal galaxies lie in this region too. This suggests that a better measurement of the K-band cluster luminosity function can be made if the field-to-field variance of the background can be measured as a function of colour. (iv) If we assume that none of the galaxies in the region of the B-K vs. B-R plane given in (iii) in our cluster fields are background, and that all the cluster galaxies with $15.5 < K < 18.5$ lie in this region of the plane, then we measure alpha = -1.41 +/- 0.35 for -19.3 < M_K < -16.3, where alpha is the logarithmic slope of the luminosity function.

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arXiv1997

The dwarf galaxy population of the Coma cluster to M_R=-11

We present the luminosity function (LF) and measurements of the scalelengths, colours, and radial distribution of dwarf galaxies in the Coma cluster down to R=24. Our survey area is 674 arcmin^2; this is the deepest and most detailed survey covering such a large area. Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are: 1) Galaxies in the Coma cluster have a luminosity function that is steep (α\sim -1.7) for -15 < M_R < -11, and is shallower brighter than this. The curvature in the LF at M_R \sim -15 is statistically significant. 2) The galaxies that contribute most strongly to the luminosity function at -14 < M_R < -12 have colours and scalelengths that are consistent with those of local dwarf spheroidal galaxies placed at the distance of Coma. 3) These galaxies with -14 < M_R < -12 have a colour distribution that is very strongly peaked at B-R = 1.3. This is suggestive of a substantial degree of homogeneity in their star formation histories and metallicities. 4) These galaxies with -14 < M_R < -12 also appear to be more confined to the cluster core (r \sim 200 kpc) than the brighter galaxies.

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arXiv1997

The galaxy luminosity function in clusters and the field

We present the results from a CCD survey of the B-band luminosity functions of 9 nine clusters of galaxies, and compare them with published photographic luminosity functions of nearby poor clusters like Virgo and Fornax and also to the field luminosity function. We derive a composite luminosity function by taking the weighted mean of all the individual cluster luminosity functions; this composite luminosity function is steep at bright and faint magnitudes and is shallow in-between. All clusters have luminosity functions consistent with this single composite function. This is true both for rich clusters like Coma and for poor clusters like Virgo. This same composite function is also individually consistent with the deep field luminosity functions of Cowie et al. (1996) and Ellis et al. (1996), and also with the faint-end of the Las Campanas Redshift Survey R-band luminosity function, shifted by 1.5 magnitudes. A comparison with the Loveday et al. (1992) field luminosity function which is well-determined at the bright-end, shows that the composite function that fits the field data well fainter than $M_B = -19$ drops too steeply between $M_B = -19$ and $M_B = -22$ to fit the field data there well.

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arXiv1997

On the enrichment of the intergalactic medium by galactic winds

Observations of metal lines in $\lyal$ absorption systems of small H~I column density and their ubiquitous nature suggest that the intergalactic medium (IGM) was enriched to about $Z \sim 0.01 \> Z_{\odot}$ by a redshift $z \sim 3$. We investigate the role of winds from small star-forming galaxies at high $z$ in enriching the IGM. The existence of large numbers of small galaxies at high $z$ follows naturally from hierarchical clustering theories (e.g. CDM). For analytical simplicity we assume that the galactic winds escape the galaxies at a single characteristic redshift $z_{in}$, and we model the galactic winds as spherical shock waves propagating through the IGM. We then calculate the probability distribution of the metallicity of the IGM, as a function of time (for different values of $z_{in}$), adopting plausible galaxy mass functions (from Press-Schechter formalism), cooling physics, star-formation efficiencies, gas ejection dynamics, and nucleosynthesis yields. We compare this expected distribution with the observed distribution of metallicities in the Ly$α$ forest at $z=3$, the metal poor stars in the halo of our Galaxy, and with other observational constraints on such a scenario. We find that galactic winds at high $z$ could have enriched the IGM to a mean metallicity of $Z \sim 0.01 Z_{\odot}$ at $z \sim 3$, with a standard deviation of the same order, if $z_{in} \la 5$, and that this satisfies all the observational constraints.

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arXiv1997

Dwarf galaxies in four rich clusters with 0.02 < z < 0.14

Deep measurements are presented of four rich clusters of galaxies: Abell 1367 (z=0.022), Abell 2199 (z=0.030), Abell 1795 (z=0.063), and Abell 1146 (z=0.141). All clusters have an excess of galaxies at faint magnitudes above blank sky fields. We correct for background contamination and measure the luminosity function of these galaxies in each cluster, and then combine these luminosity functions to get better statistics. The resultant combined luminosity function is rising at faint magnitudes, with a logarithmic slope -1.5 < α< -1.2 for -18 < M_B < -13 and -19 < M_R < -15. This is similar to what has been observed independently in the Coma cluster. The colours of these faint galaxies suggest that they are dwarf spheroidals.

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arXiv1996

The luminosity function of dwarf galaxies in four spiral-rich groups

We measure luminosity functions in the cores of four spiral-rich, poor clusters of galaxies at median redshift $z = 0.016$. In the red magnitude range -14 < M_R < -10, our data imply that the luminosity functions phi(L) \propto L^{alpha} are steep, -1.8 < alpha < -1.6, in the central 200-300 kpc of Abell 262 and of the NGC 507 Group. Abell 194 also shows signs of a steep luminosity function, alpha < -1.6, in this magnitude range. In Pegasus, the dwarf galaxy density is too low to let us constrain alpha. The NGC 507 Group and Abell 194 have been interpreted as clusters that are forming today, based on morphology and velocity structure. The high spiral galaxy fraction in Abell 262 relative to clusters like Virgo and Coma also suggests that it is young. We therefore suggest that steep luminosity functions in the range -14 < M_R < -10 may be a universal feature of young clusters and possibly of the field. If this is true, then the observed paucity of gas-rich galaxies in such environments suggests that we are finding galaxies similar to the low-surface-brightness, dark-matter-dominated dwarf spheroidal galaxies seen locally and in Virgo. This interpration is also consistent with the distribution of colors and sizes of the faint galaxies in Abell 262. If we are indeed detecting dwarf spheroidal galaxies and if they are as numerous relative to bright galaxies in the field as they are in the young clusters observed here, then the contribution of their halos to the cosmological mass density is Omega_{dSph halo} \approx 0.01. This is much smaller than values of Omega derived from dynamical measurements.

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arXiv1996

A candidate supernova in the ultraluminous galaxy IRAS 12112+0305

We report the discovery of a candidate supernova in the ultraluminous galaxy IRAS 12112+0305 during April/May 1995. This would be the first supernova discovered in an ultraluminous galaxy with L_IR > 10^12 L_sun, although supernovae have been discovered in the slightly less extreme starburst galaxy NGC 3690. If this is a supernova, our very limited observations suggest that it is a Type II.

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arXiv1995

How much of the extreme luminosity of IRAS F10214+4724 can be attributed to gravitational lensing

\noindent The galaxy IRAS F10214+4724, discovered in a spectroscopic survey of a 0.2 Jy sample by Rowan-Robinson and collaborators in 1991, is significantly more luminous than any other known galaxy. Its bolometric luminosity is comparable to those of the most luminous quasars. Recent obsservations have revealed a candidate foreground group of galaxies, which might gravitationally lens F10214+4724, thus explaining much of its luminosity. High-resolution imaging of F10214+4724 has revealed that most of its near-IR flux comes from a circularly symmetric arc; this also supports the gravitational lens interpretation. In such a scenario, F10214+4724 would be the high-redshift analogue of the ultraluminous IRAS galaxies observed locally. This work presents a simple statistical lensing model to investigate this possibility.

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