Integral field spectroscopy in the IR: Gemini-CIRPASS observations and the star-formation history in the nucleus of M83

While HST offers excellent spatial resolution, broad band photometry cannot tell the whole story for a number of reasons:

• It is subject to dust bias as the reddening vector parallels much of the evolutionary track

• Biased against young star-forming regions which may have strong line emission but weak continuum

• Instantaneous burst and continuous star-formation models are degenerate in colour space

Long slit spectroscopy can overcome some of these problems, but introduces a bias based on the selection of targets for follow-up.

Observations were performed over two nights during April 2003. The 0.36arcsec IFU lens scale was used to observe three telescope pointing in the central nuclear starburst region of M83. Each pointing was observed, in both the J and H bands, with 2x900sec exposures on target, interleaved with offset sky frames.

Here we see the three colour (F300W,F547M,F814W) HST/WFPC2 image of Harris et al. 2001 ApJ 122 3046. The three CIRPASS IFU points are overlaid.

[FeII] 1.64mPa 1.28 m

Emission line maps are created by profile fitting the spectrum recorded by each lens in the IFU. The equivalent width map for Pa in the J-band and H-band [FeII] 1.644m are shown here. The IR observations penetrate the prominent dust lane, seen in the WFPC2 image.

CIRPASS, The Cambridge Infra-Red Panoramic Survey Spectrograph, is a Fiber fed multi-mode IR J+H band spectrograph. In multi-object mode CIRPASS offers 150 object MOS spectroscopy over a field of view in excess of 20arcmins. A multi-IFU MOS mode will be commissioned in 2005. The CIRPASS wide field Integral field mode implements a 490 element macro lens array giving a field of view of 13x9arcsec at 0.36arcsec resolution. Intermediate resolution spectra (R~4000, working between the bright night sky OH lines) are recorded on a 2Kx2K Hawaii-2 IR array.

Using the STARBURST99 models of Leitherer et al. and the Pa and [FeII] 1.644m emission lines we see a clear trends to the star-formation history across the central region of M83, a continuous star-formation model is not well suited to the observations.

6.2 Myr

6.5 Myr

7.6 Myr

7.6 Myr

10.6 Myr

We present Gemini-South observations of the nuclear starburst region of M83 from the CIRPASS near-IR integral field spectrograph. Spectroscopic diagnostics are used to overcome many of the uncertainties inherent in photometric studies of the star-formation history of the central region of M83. We use Pa and [FeII] emission, along with absorption in the CO(6,3) band head, to demonstrate an age gradient, as oppose to stochastic star-formation, across the nuclear star-forming region of M83.

Robert Sharp and Stuart Ryder AAO

Johan Knapen U. Hertfordshire

Lisa Mazzuca GSFC

Ian Parry U. Cambridge

SummarySummary• Photometry gives an incomplete/ambiguous age picture.Photometry gives an incomplete/ambiguous age picture.• NIR IFU spectroscopy is less biased by extinction and NIR IFU spectroscopy is less biased by extinction and selection effects.selection effects.• Multiple independent spectral line diagnostics help constrain Multiple independent spectral line diagnostics help constrain Star Formation Star Formation HistoryHistory..• Circumnuclear Star Formation in M83 takes place in short-Circumnuclear Star Formation in M83 takes place in short-lived, high-efficiency bursts (rather than continuous mode), lived, high-efficiency bursts (rather than continuous mode), consistent with scarcity of gas in ring.consistent with scarcity of gas in ring.• Clear azimuthal age gradients in M83 (and M100, Clear azimuthal age gradients in M83 (and M100, Ryder, Knapen & Takamiya 2001 MNRAS 323 663) argue for gas ) argue for gas fuelling via bar, and sequential triggering.fuelling via bar, and sequential triggering.

SMA CO(J=3-2)Sakamoto et al. astro-ph/0403145

Molecular gas traces the dust lane but is scares in the older regions of star-formation.

J-band spectrum of Knot 10 from Harris et al. 2001

OH sky emission

H-band spectrum