Star formation outside galaxies undergoing gravitational and hydrodynamic interactions: dust attenuation and the star formation rate

TL;DR

This study compares dust attenuation and star formation in star-forming knots outside galaxy disks formed by hydrodynamic (ram-pressure stripping) and gravitational (collisional ring and tidal tails) perturbations, using high-resolution UVIT imaging. Dust attenuation is quantified from the UV continuum slope derived from FUV−NUV colors, and SFRs are corrected accordingly to yield intrinsic SF rates in individual knots. Across the four targets, the attenuation ranges and dust-corrected SFR densities in jellyfish tails, the NGC 5291 collisional ring, and the NGC 7252 tidal tails are broadly similar, though the jellyfish tails show both very dust-poor and dust-rich knots, with SFR densities comparable to gravitational debris. The results imply that extragalactic star formation in debris structures is robust to perturbation type, though local gas and dust conditions modulate SFE and dust processing in these environments, informing models of galaxy evolution in dense environments.

Abstract

Galaxies undergo perturbations, either gravitational or hydrodynamic in origin, which can generate extragalactic structures such as rings and tails, where in situ star formation may take place. We selected a sample consisting of JO201 and JW100, undergoing ram-pressure stripping, and NGC 5291 and NGC 7252, formed through gravitational interactions, to investigate how different perturbation mechanisms influence dust content and star formation in extragalactic features. In both cases, star formation can be observed outside the main disks of the galaxies. We present new results of dust attenuation for JO201 and JW100, while for NGC 5291 and NGC 7252 we use results from our previous study, based on high-resolution observations obtained with the Ultraviolet Imaging Telescope onboard AstroSat. Dust attenuation is determined from the ultraviolet continuum slope ($β$) calculated using the FUV-NUV colour, and the star formation rates of the star-forming knots are corrected accordingly. It is seen that dust attenuation and dust-corrected SFR densities of the knots in the ram-pressure stripped tails of JO201 and JW100 are comparable to those in the collisional ring of the NGC 5291 system and the tidal tails of the NGC 7252 system. We conclude that, though the formation scenarios of the tails of JO201 and JW100, the NGC 5291 ring, and the NGC 7252 tails are different, their dust content and star formation activity are notably similar.

Figures (12)

• Figure 1: Colour composite images of JO201 (top) and JW100 (bottom) made using FUV (blue), NUV (green) and DECaLS r-band image (red).
• Figure 2: Colour composite images of the NGC 5291 (top) and NGC 7252 (bottom) systems made using FUV (blue), NUV (green) and DECaLS r-band images (red).
• Figure 3: UVIT images of JO201 (top) and JW100 (bottom). The contrast level is adjusted to highlight the features.
• Figure 4: FUV images of JO201 (top left) and JW100 (bottom left) with SF knots marked in red. The segmentation maps of JO201 (top right) and JW100 (bottom right) are shown in the right. The colours of the segments indicate the relative brightness of SF knots with brighter SF knots corresponding to darker shades of brown. z-band isophotes corresponding to 22 mag/arcsec$^2$ shown (green-dashed contours).
• Figure 5: Distribution of NUV-r colours of the SF knots in the tails of JO201 and JW100