UNITED KINGDOM INFRARED TELESCOPE Newsletter Issue 14, Spring 2004 Massive Galaxy Formation in Dense Environments Jason Stevens1, Rob Ivison1, Mat Page2 & Ian Smail3 1. Astronomy Technology Centre, Edinburgh, U.K. 2. Mullard Space Science Laboratory, University College London, U.K. 3. Institute for Computational Cosmology, University of Durham, U.K. During the last 2 semesters we have targetted the fields of X-ray absorbed QSOs at z=1.5-3 as sites of biased galaxy formation. Our SCUBA images show that these regions are overdense in ultraluminous star-forming galaxies, with both the QSO and several companions detected in each field. The dust emission in these systems is extended on galaxy-wide scales (50-100 kpc) and the individual galaxies are distributed in a structured manner within the fields. These observations appear to be in accord with predictions of the popular hierarchical model in which large scale structure builds through galaxy mergers along filaments, with the most massive structures -- clusters -- forming at the intersections (as signposted by the QSO).   FIGURE 1: UFTI K-band image overlayed with 450 micron signal-to-noise contours from SCUBA. Contours start at 2-sigma and increase in 1-sigma steps. The z=1.8 QSO is the northern-most source. The filament of star-forming galaxies extends over ~400 kpc. FIGURE 2: Postage stamp images of the 450 micron sources. Most possible counterparts are EROs. The magnitudes of these counterparts are (a) K=19.3, (R-K)=5.8 (b) K=19.9, (R-K)=5.3 (c) K=20.3, (R-K)=3.9 (d) K>21.6, (R-K)<3.6 (e) K=18.8, (R-K)=5.4 (f) K=20.4, (R-K)=4.6. In May 2003 we obtained a deep (3-sigma ~ 21.6) K-band image of one of these fields with UFTI through the UKIRT Service Programme. The field is centred on the z=1.8 QSO RXJ094144.51+385434.8 which shows a striking filament of star-forming galaxies at 450 microns. Less than one such galaxy, besides the QSO, would be expected for a random field, so this structure represents an approximate order of magnitude over-density. Our goals were threefold: (1) to find counterparts for follow-up spectroscopy with Gemini/GMOS, (2) to measure the colours of possible counterparts since submillimetre-selected galaxies can be identified as EROs, and (3) to search for merger activity on smaller spatial scales than probed with SCUBA (~8.5" at 450 microns). In Fig.1 we show the K-band image overlayed with the SCUBA 450 micron signal-to-noise contours. In Fig.2 we show postage stamp images of the individual 450 micron sources with corresponding K- and R-band data (the latter from the WHT). With the exception of the nearest companion to the QSO, all sources have possible counterparts identified as EROs (with (R - K) > 5.3). The southern-most 450 micron source has an optical/near-infrared counterpart with the appearance of an advanced merger with one ERO component and one relatively blue component. These observations have allowed us to secure the Gemini/GMOS time required to measure their spectroscopic redshifts -- the only robust method of locating them in a structure with the QSO. A journal paper on this work has been submitted to ApJL. We argue that the galaxies in this structure will evolve into the population of luminous elliptical galaxies found today in the core regions of all rich galaxy clusters. UKIRT discovers dust in a type Ia supernova R. Kotak1, W.P.S. Meikle1, A. Adamson2 & S. Leggett2 1. Imperial College, Blackett Lab., London, UK. 2. UKIRT/Joint Astronomy Centre, Hilo, Hawaii, USA A long-standing mystery about type Ia supernovae (SNe Ia) is the nature of their progenitor(s). Although there is a general consensus that the progenitor must involve at least one carbon-oxygen white dwarf, there are few - if any - constraints on the half dozen or so progenitor channels that have been proposed. FIGURE 1: UIST K-band image of SN 2002ic with the host galaxy lying ~5'' to the east. One of the defining observational characteristics of type Ia supernovae is the absence of a spectral signature of hydrogen. This has posed problems for the single-degenerate scenario, in which a white dwarf grows to the Chandrasekhar mass by accreting from a non-degenerate (and presumably hydrogen-rich) companion. In June 2003, evidence for H-α emission associated with the type Ia SN 2002ic was announced by Hamuy et al. (2003). They found that the optical spectra of SN 2002ic exhibited similar characteristics to those of `normal' type Ia SN, albeit with diluted features. Strong and persistent emission from H-α was also evident. However, only a few weeks later (+70 days), SN 2002ic underwent an astonishing metaphorphosis into the spectral form of a type IIn supernova (a type II supernova with narrow emission lines). From an echelle spectrum obtained with the VLT, we found that the H-α profile actually comprised a narrow (~100 km/s) P Cygni-like profile atop a broad base (Kotak et al. 2004). Thus, in SN 2002ic we were witnessing the first-ever interaction of a SN Ia with circumstellar material. In late August last year, SN 2002ic produced another surprise. Given the type IIn spectral metamorphosis, we conjectured that, as with bona-fide type IIn events (e.g. SN 1998S: Gerardy et al. 2002, Meikle et al. 2003), SN 2002ic might develop a strong near-IR excess. We therefore obtained a K-band magnitude measurement with UIST on August 27, yielding K = 18.00(+/- 0.05). Further H and K-band photometry obtained with UFTI in late December last year showed that the supernova had brightened in K to +17.76. Assuming a distance of 290 Mpc, this corresponds to a huge K-band luminosity - about twice as luminous as the nearby type IIn SN 1998S (Meikle et al. 2003) and more than a hundred times more luminous than a typical type Ia supernova at the same phase (about 290 days post-explosion). We believe that the source of the IR emission is pre-existing dust in the circumstellar medium (CSM), heated by the ejecta/CSM shock interaction. We rule out dust condensation in the ejecta. Even at the maximum dust evaporation temperature of ~1500 K the K-band luminosity would require a source at a radius >1000 AU (corresponding to a velocity >6000 km/s at this epoch) which is much too far out in the ejecta to be a plausible region of grain formation. Thus, not only have we demonstrated the presence of a slow-moving wind associated with a type~Ia event, we have also shown that it is dusty. As dust has never before been associated with a type Ia supernova, this raises the intriguing possibility that at least some type IIn supernovae may actually be type Ia supernovae, and that they, or their progenitors, may be significant contributors to interstellar dust. References Gerardy et al., 2002, ApJ, 575, 1007 Hamuy, M., Phillips, M. M., Suntzeff, N. B., et al. 2003, Nature, 424, 651 Kotak, R., Meikle W.P.S. et al., 2004 (to be submitted) Meikle et al. 2003, Proc. ESO/MPA/MPE Workshop, astro-ph/0211144 High resolution water spectra of low mass stars using Michelle Nikki Davies1, Serena Viti1, Hugh R A Jones2, Jonathan Tennyson1 & Steve Miller1 1. Department of Physics and Astronomy, UCL , Gower St., London, WC1E 6BT, UK 2. Liverpool John Moores University, Byrom St. Liverpool,L3 3AF, UK Introduction Low mass stars (LMS) constitute ~ 80% of our stellar neighbourhood by number. Their spectra are extremely rich in structure and their opacity is made up of many molecular and atomic absorbers, each with hundreds-of-thousands to millions of spectral lines. This means that colours are not a reliable diagnostic of their properties. The determination of their fundamental parameters rely both on a direct empirical comparison among stars of similar spectral types and on a careful fit to synthetic spectra. The effective temperature of LMS has frequently been investigated, but it is still not well determined. It is well known that water vapour is extremely sensitive to effective temperature and therefore it could potentially be used as a tool to derive an effective temperature scale. However, there has been a long-standing discrepancy between empirical effective temperatures and those derived by synthetic spectra (e.g., Jones et al. 1996). This is primarily due to the lack of a complete inclusion of water opacity in the models. Modelling LMS atmospheres in the near-infrared is not a trivial task: water vapour dominates this part of the spectrum and at the effective temperatures applicable to cool star atmospheres (< 4000 K) water can access energies as high as 45000 cm-1 before it dissociates; to reproduce high temperature water spectra is very challenging because of the complexity of the motion of asymmetric triatomic molecules. Recently Leggett et al. (2001) used a new synthetic grid which includes the water line-list calculated by Partridge & Schwenke (1997) to determine fundamental parameters for a large sample of LMS. They conclude that problems remain with the match of the observed water bands. The main sources of error in present water opacity databases are the incorrect high temperature transitions. This is extensively confirmed by recent work (Jones et al. 2002) in the 2.5-3.0 micron region where ISO observations of water vapour in a sample of M dwarfs is compared with synthetic spectra. FIGURE 1: Example of water line assignments in the mid infrared spectrum of the M giant BS337. Some lines have been identified as water lines but no quantum assignment has been done yet. .Most assignments are blended transitions (marked with an *): *1 11.1830 2712,15-2611,16 (110-110) 11.1826 2625,2-2524,1 (110-110) 11.1824 not assigned ....... *2 11.1869 2622,4-2522,5 (001-001) 11.1864 2519,6-2418,7 (000-000) 11.1859 2621,5-2520,6 (001-001) 11.1857 not assigned ....... *3 11.1945 2712,16-2611,15 (010-010) 11.1940 not assigned ....... *4 11.1967 2423,2-2322,1 (020-020) 11.1961 183,15-172,16 (001-001)

Although the strongest water vapour opacity is at shorter wavelengths, analysis of sunspots shows that H2O accounts for the majority of lines in the region between 8 and 21 microns. In this spectral region the water transitions are largely pure rotational ones, in contrast to the vibration-rotation transitions which dominate the spectrum at shorter wavelengths. The use of pure rotational transitions greatly simplifies the spectral analysis as estimates of the transition strengths are much more straightforward. Furthermore, the presence of pure rotational transitions within different vibrational states, which is characteristic of the sunspot spectrum, yields a large dynamic range for temperature analysis.

This article describes a first attempt at measuring water bands in the mid-IR region of a sample of M stars.

Observations, preliminary results and future work

During the nights 11-13 August 2002, we observed a sample of late-type stars using Michelle on the UKIRT. Although ultimately our aim is to measure water vapour in M stars and brown dwarfs, the sensitivity of Michelle at the time led us to choose a sample primarily composed of brighter objects, such as M giants and K dwarfs. The echelle grating of Michelle was positioned to obtain the spectral range 11.18-11.21 microns, with R ~ 15000. This spectral range was chosen because of the relatively small telluric contamination and high sensitivity of water lines.

The aim of this study is the use of high resolution observations of individual rotational water vapour lines to determine the effective temperatures for M stars. A first step toward this is the identification of water lines in the observed spectra. Our first attempt at data reduction was done for two stars, BS8316 (M2I) and BS337 (M0III). This led to a good signal to noise spectrum, although we could not reliably remove the telluric contamination of the Earth's atmosphere. This was due to the relatively poor signal-noise of our standard star spectra. Thus, we performed a careful analysis of the observed spectra and with the aid of the Hitran database we found that, as predicted, this region was quite free of telluric contamination; we manually removed the very few lines that were found to be telluric candidates.

We then performed a line assignment using sunspot spectra in the same spectral region. We found a good correspondence between our two stars' spectra and the sunspot spectrum (T ~ 3200K) which indicated that indeed M star spectra from 11.18-11.21 microns are characterized by several water vapour transitions. In Figure 1 we show some of our preliminary identifications. This is the first time that water transitions have been assigned in this region of the spectrum for M stars.

We are now in the process of determining which of the assigned water transitions are most sensitive to small effective temperature changes. This can be done in two steps: 1) we will make use of two water line-lists, the Partridge & Schwenke (1997) line-list and the newly computed BT1 (Barber et al. in prep), to construct a grid of spectra at several temperatures spanning the range covered by M stars. A careful analysis of this grid will yield a list of temperature-sensitive water transitions. These can then be directly used to determine the effective temperature of our stars. 2) Detailed models of M stars will be performed using the PHOENIX NextGen code of Hauschildt et al. (1997). This grid of models will be computed using the new line-list BT1. We will then combine our spectral analysis, assignments, theoretical estimates of line strengths and detailed models to derive an effective temperature scale.

We envisage that the sensitivity of our water-transition derived temperatures will be an important constraint on the long running discrepancy in effective temperature scales for low mass stars, between those derived by empirical methods and those derived by comparison of synthetic and observational spectra in the optical and near-infrared. In the longer term we would like to extend this study to cooler, and fainter, brown dwarfs.

References
Jones H R A,, Longmore A J, Allard F, Hauschildt P H, 1996, MNRAS, 280, 77
Leggett S K, Allard F, Geballe T R, Haushildt P H, Schweitzer A, 2001, ApJ, 548, 908
Partridge H, Schwenke D W, 1997, JChem Phys, 106, 4618
Jones H R A, Pavlenko Y, Viti S, Tennyson J, 2002, MNRAS, 330, 675
Hauschildt P H, Baron E, Allard F, 1997, ApJ, 483, 390

1. Dept. of Physics, University of Durham, U.K.
2. Astronomy Dept., California Institute of Technology, USA
3. U.K. Astronomy Technology Center, Edinburgh, U.K.

Introduction

The problem with current galaxy formation theories is not our understanding of why galaxies form (this is due to radiative cooling of diffuse gas), but why only a small fraction of baryons have been locked into stars. Galaxy formation models that only include cooling condense more than 5 times too many baryons into stars. An additional layer of physics (generically called ``feedback'') is missing from their models. The nature of this process is so far unclear, but observations of high redshift galaxies have hinted at an answer.

The solution may arise from stellar winds and supernovae in high star formation rate (SFR) galaxies, the energy from which can cause an expanding shell of material to burst out of the galaxy disk and become a ``superwind'' traveling through the IGM. Observations of this phenomenon at high redshift manifest themselves as a redshift offset between the UV emission lines (the Ly-α (λ 1215 AA) emission line which is resonantly scattered from the shell of expanding material), the strong UV absorption lines (such as CIV(λ 1549 AA), SiII (λ1309 AA)) which trace the galaxy ISM, and the redshift of the nebular emission lines (such as Hα) which trace the star forming population. The velocity offset is frequently as high as 600 km/s --- far greater than the escape velocity of the galaxy. A simple model is then one where proto-galaxies drive a blast wave out into the surrounding inter-galactic medium. If the interpretation of the data as an expanding shell is correct, then the material will escape the galaxy's dark matter halo and play no further role in galaxy formation.

It is not surprising that Ultra Luminous Infra Red Galaxies (ULIRG's) show signs of these starburst driven superwinds since the far infra-red luminosity of a galaxy is a clear indication of vigorous star formation activity in these galaxies. Such galaxies are known to have SFRs of 100's of solar masses per year - sufficient to drive strong superwinds.

A particularly striking case of this signature is seen in Elais N2 850.4 at z=2.38. From multi-wavelength long-slit observations Smail et al. (2003) conclude that this ULIRG is a two-component merging system, the energy from the merger causing a massive burst of star formation. The velocity offsets from the long-slit data hint at a large scale outflow from this system, but the data is very difficult to interpret since the long-slit observation only gives a cross section through the galaxy. By exploiting an Integral Field Unit (IFU) observation of the galaxy we can obtain a clearer indication of the dynamics of the system, since the IFU gives a 3-dimensional picture of the galaxy (in x, y and wavelength/velocity).

UIST IFU observations of Elias N2 850.4

In May 2003, we observed Elias N2 850.4 for a total of 8 hours using the HK grism and the UIST IFU. We observed both the H&α;(λ6562.8 AA) and OIII(λ5007 AA) emission lines and used the ORAC-DR data reduction pipeline to extract, flat-field and wavelength calibrate the data. The resulting velocity field from the Hα emission lines shows 2 merging systems, offset by ~400 km/s (Fig.1). The OIII emission line is offset by 1.5" from the centre of the Hα and blue-shifted by 700 km/s. (We later confirmed the spatial offset with an IRTF narrow-band observation (Swinbank et al. 2004, in prep.).) The lower S/N in the OIII means we do not see any velocity structure in this emission line. A simply interpretation of the OIII offset is that one of the merging components is driving an AGN, which we observe in OIII.

FIGURE 1: The UIST IFU observations of Elais N2 850.4. The colour scale represents the strength of the Hα emission (detected with a S/N>5) while the contours map the velocity structure. Notice the ~400 km/s shift across this merging galaxy. The triangle marks the centre of the OIII emission, offset by ~1" and 700 km/s blueward of the Hα. A possible interpretation of these data is that the merging galaxies are driving an AGN which is detected in OIII.			FIGURE 2: Combining the UIST IFU observations with GMOS IFU data. The colour scale shows the Lyα emission (detected with a S/N>3 at Gemini) while the contours are colour coded to represent the velocity field of the Hα UIST data (blue-shifted and red-shifted) evident in Fig.1.

Further analysis of this system has come from a GMOS IFU Demonstration Science observation taken in June 2002. By combining the UIST results with a Lyα emission line map from GMOS IFU we are also able to probe the dynamics of the expelled material being driven into the IGM (Fig.2). Aligning the emission line maps from the UIST and GMOS IFU observations by a careful comparison of astrometry solutions (from Hα narrow and broad K-band imaging to V-band (rest frame UV) imaging), we find the UV continuum detected with the GMOS IFU is coincident with the centre of the Hα detected in the UIST IFU data. We have determined that the 2 merging components of the galaxy are further offset from the velocity of the Lyα emission line (which is hinted at in the long-slit observations from Smail et al. 2003). The redshift of this line places it directly between the velocities of the 2 merging components. A second (lower intensity) Lyα emission line at +700 km/s is also seen behind the merger. If we are to interpret the data in terms of an 'expanding shell' model, then a shell of neutral gas is being ejected from one of the two merging components and is at the same time being illuminated by a strong starburst. This scenario is illustrated in a cartoon in Fig.3.

FIGURE 3: A cartoon showing the complex structure seen in Elais N2 850.4. The two merging galaxies (observed in Hα with the UIST IFU - drawn in red above) are separated by ~450 km/s and offset spatially by ~2". The GMOS IFU observations then show two Lyα emission line regions (coloured green). These are shells of neutral gas which are being driven out of one of the galaxies. The brightest Lyα region appears directly between the two merging galaxies. The OIII emission also seen in the UIST IFU data is offset by 1.5" from the Hα emission region and by -700 km/s. The OIII emission is probably caused by an AGN in one of the merging starburst galaxies.

Although our analysis is still in its early stages, the data do show that IFU observations of high-redshift proto-galaxies can be used to study these superwinds. Further objectives also include a study of the metallicity and obscuration by comparing the ratio's of Hα/Lyα.

Acknowledgements: We would like to thank Sandy Leggett and Watson Varricatt for their assistance with the UIST IFU observations, and Richard Bower, Andy Bunker and Joanna Smith for their help with the GMOS observations.