---
abstract: 'We have used ESO’s new NIR IFS SINFONI during its Science Verification period to observe the central regions of local starburst galaxies. Being Science Verification observations, the aim was two-fold: to demonstrate SINFONI’s capabilities while obtaining information on the nature of starclusters in starburst galaxies. The targets chosen include a number of the brighter clusters in NGC1808 and NGC253. Here we present first results.'
address: 'ESO, Karl-Schwarzschild-Straße 2, D-85748 Garching bei München, Germany'
author:
- 'Lowell E. Tacconi-Garman'
title: SINFONI Observations of Starclusters in Starburst Galaxies
---

galaxies: individual (NGC253, NGC1808); galaxies: starburst; galaxies: star clusters; infrared: galaxies 97.10.Bt ,98.54.Ep ,98.62.Ai

Introduction
============

That star formation in starburst galaxies manifests itself in the production of numerous young, massive, clusters or super-starclusters is by now observationally quite well established (e.g. [@TGSE]; [@Mengel05] and references therein; [@deGrijs]). At least in part owing to the strong, patchy obscuration in these systems the nature of these clusters is less well known, especially with respect to their age, mass, boundedness and the likelihood of their survival (but see, for example, [@Mengel05] and [@Gieles05]). We have made short observations of near- and circumi-nuclear fields in two nearby starburst galaxies, NGC253 and NGC1808, during SINFONI Science Verication. We are using these data to better characterize the central starburst regions and starclusters in these systems. Here we present a brief summary of initial results.

SINFONI and Observation Overview
================================

SINFONI, offered to the community since 01 Apr. 2005, is a combination of a NIR Integral Field Spectrometer (SPIFFI) and a MACAO adaptive optics module. Briefly, SPIFFI, uses gratings to provide the user with data with a spectral resolution of 2000, 3000, 4000 (in the J, H, and K Bands, respectively), or 1500 for the combined H+K Bands. The spatial sampling of 64$\times$32 pixels over square fields-of-view 0.8$^{\prime\prime}$, 3$^{\prime\prime}$, or 8$^{\prime\prime}$ on a side is achieved by slicing the field with a mirror-pair image slicer and imaging it onto a Hawaii 2RG detector. The largest of these fields-of-view is meant primarily seeing-limited operation, as is the case in the absence of a suitable adaptive optics reference target.

The MACAO unit is very broadband in its response, though is peaked in the R Band. Although targets with R magnitudes less than about 11 yield the best corrections, some correction can be achieved to R$\sim$17 under the best conditions. In very good conditions moderate improvement can be achieved even to 30$^{\prime\prime}$ separation between the AO-target and the science target[^1].

The observations reported on here were made with the H+K grating and the 0.8$^{\prime\prime}$ (NGC253; two fields with 200 and 480 sec exposures) and 0.8$^{\prime\prime}$ (NGC1808; two fields with 10 and 20 min exposures) pixel scales. The NGC1808 observations used the MACAO unit, while the NGC253 observations were done in seeing-limited mode.

First Results
=============

Br$\gamma$ and He[I]{} in NGC253
--------------------------------

In Figure 1 we present images of the log of the Br$\gamma$ emission (left), the log of the equivalent width of Br$\gamma$ (center), and the ratio of the 2.058$\,\mu$m 2$^1$P–2$^1$S He[I]{} line to Br$\gamma$ (right) in the circumnuclear region of NGC253. The Br$\gamma$ is seen to peak strongly at the position of the well-known IR peak in this galaxy to the SW on the nucleus, consistent with what is seen in Pa$\alpha$, Br$\delta$, and 2.058$\,\mu$m 2$^1$P–2$^1$S He[I]{} (not shown).

Although the 2.058$\,\mu$m 2$^1$P–2$^1$S He[I]{} line is not an ideal tracer of the hardness of the radiation field ([@Lumsden2001],[@RigbyRieke04]), its ratio with Br$\gamma$ and the EW$_{\mathrm Br\gamma}$ in the two peaks shown in Figure 1 (right) are consistent with starburst age of  5.5Myr with the most massive stars being $\sim$30M$_\odot$. This is less massive than postulated by some authors for the bright peak to the SW of the nucleus, but the resulting radiation field is likely consistent with what would be required to explain the strong decrease in the 3.3$\,\mu$m PAH feature-to-continuum ratio at these positions [@PAH]. Observations of a “pure” line[^2] of He[I]{}, such as the 1.7007$\mu$m 4$^3$D–3$^3$P line [@Lumsden2001], would be useful to properly constrain this scenario.

A Comparison with [*HST*]{} NICMOS
----------------------------------

As a means of demonstrating the combined capabilities afforded by both the VLT-UT4 and SINFONI itself, we present in Figure 2 an image of the 1.644$\,\mu$m \[Fe[II]{}\] line emission from NGC253 as observed with SINFONI. This region has been previously observed in the same line with [*HST*]{} NICMOS [@Alonso-Herrero2003], and the contours in Figure 2 are derived from that data. The correspondence is quite remarkable indeed, especially considering that the SINFONI data are seeing-limited. However, the true advantage of SINFONI over [*HST*]{} NICMOS lies in the wealth of information afforded by the IFS itself (through velocity (dispersion) maps, not shown here due to space limitations).

Star clusters in NGC1808
------------------------

The data from our AO-assisted observations of two clusters in NGC1808 are a bit noisier than those of NGC253, which compromises (at least thus far) our ability to construct fruitful line maps. However, in Figure 3 we present collapsed K-Band images of the fields observed, with each of the two right panels being 0.8$^{\prime\prime}$ on a side. We have used our best guess at the PSF (from the telluric calibration star) and infer an upper limit on the size of these clusters of 15pc and 8pc for Knots 20 and 12 (Figure 3 top right, and bottom right), respectively. This is broadly consistent with the sizes quoted in [@TGSE].

[999]{} Alonso-Herrero, A. et al., 2003, [ *AJ*]{}, [**125**]{}, 1210 de Grijs, R., this volume Gieles, M. et al., 2005, [*astro-ph/0506066*]{} Johnson, K.E. et al., 2001, [*ApJ*]{}, [ **559**]{}, 864 Lumsden, S.L., Puxley, P.J., and Hoare, M.G., [*MNRAS*]{}, [**320**]{}, 83 Rigby, J.R. and Rieke, G.H., 2004, [*ApJ*]{}, [**606**]{}, 237 Mengel, S., et al., 2005, [*astro-ph/0505445*]{} , L.E., Sternberg, A., and Eckart, 1996, [*AJ*]{}, [**112**]{}, 918 , L.E. et al., 2005, [*A&A*]{}, [**432**]{}, 91 Ulvestad, J.S. and Antonucci, R.R.J. 1997, [*ApJ*]{}, [**488**]{}, 621

[^1]: Further details for SINFONI can be found on the ESO SINFONI webpage, [http://www.eso.org/instruments/sinfoni/index.html]{}, and on pages linked to from that page.

[^2]: One for which the line strength is determined almost solely from the recombination cascade physics.
