Pᵉtɘr Wᵉil8acher
Evelyn Johnston led the paper on the discovery of an "off-center compact source" in the giant LSB galaxy Malin 1 based on the existing MUSE data, now accepted at A&A.
https://arxiv.org/abs/2404.04099
#musevlt #Malin1 #LSBgalaxy
A MUSE View of the Core of the Giant Low Surface Brightness Galaxy Malin 1

Aims. The central region of the Giant Low Surface Brightness galaxy Malin 1 has long been known to have a complex morphology with evidence of a bulge, disc, and potentially a bar hosting asymmetric star formation. In this work, we use VLT/MUSE data to resolve the central region of Malin 1 in order to determine its structure. Methods. We use careful light profile fitting in every image slice of the datacube to create wavelength-dependent models of each morphological component, from which we could cleanly extract their spectra. We then used the kinematics and emission line properties from these spectra to better understand the nature of each component extracted from our model fit. Results. We report the detection of a pair of distinct sources at the centre of this galaxy with a separation of ~1.05", which corresponds to a separation on sky of ~1.9 kpc. The radial velocity data of each object confirms that they both lie in the kinematic core of the galaxy, and analysis of the emission lines reveals that the central compact source is more consistent with being ionized by star formation and/or a LINER, while the off-centre compact source lies closer to the separation between star-forming galaxies and AGN. Conclusions. This evidence suggests that the centre of Malin 1 hosts either a bar with asymmetric star formation or two distinct components in which the off-centre compact source could either be a star-forming clump containing one or more star clusters that is in the process of falling into the core of the galaxy and which will eventually merge with the central NSC, or a clump of gas infalling into the centre of the galaxy from either outside or from the disc and triggering star formation there.

arXiv.org
Apr 17, 2024 at 10:10amWeb
Show threadPᵉtɘr Wᵉil8acherApr 17, 2024
The off-center source seems to be ionized mostly by star-formation (with a bit of shocks?), forming ~25x more stars than the nucleus. It could be a young star cluster to soon merge with the main nucleus.
#Malin1 #musevlt
Show threadPᵉtɘr Wᵉil8acherApr 17, 2024
This (Johnston et al., https://arxiv.org/abs/2404.04099) is already the 2nd paper on the partial MUSE data of #Malin1 (following Junais et al., https://www.aanda.org/articles/aa/full_html/2024/01/aa47669-23/aa47669-23.html).
Fingers crossed that we'll finally get the remaining 3/4 now that we have shown how useful it is.
#musevlt
A MUSE View of the Core of the Giant Low Surface Brightness Galaxy Malin 1

Aims. The central region of the Giant Low Surface Brightness galaxy Malin 1 has long been known to have a complex morphology with evidence of a bulge, disc, and potentially a bar hosting asymmetric star formation. In this work, we use VLT/MUSE data to resolve the central region of Malin 1 in order to determine its structure. Methods. We use careful light profile fitting in every image slice of the datacube to create wavelength-dependent models of each morphological component, from which we could cleanly extract their spectra. We then used the kinematics and emission line properties from these spectra to better understand the nature of each component extracted from our model fit. Results. We report the detection of a pair of distinct sources at the centre of this galaxy with a separation of ~1.05", which corresponds to a separation on sky of ~1.9 kpc. The radial velocity data of each object confirms that they both lie in the kinematic core of the galaxy, and analysis of the emission lines reveals that the central compact source is more consistent with being ionized by star formation and/or a LINER, while the off-centre compact source lies closer to the separation between star-forming galaxies and AGN. Conclusions. This evidence suggests that the centre of Malin 1 hosts either a bar with asymmetric star formation or two distinct components in which the off-centre compact source could either be a star-forming clump containing one or more star clusters that is in the process of falling into the core of the galaxy and which will eventually merge with the central NSC, or a clump of gas infalling into the centre of the galaxy from either outside or from the disc and triggering star formation there.

arXiv.org
Show threadKnud JahnkeApr 17, 2024

@PWei888

Just remember that "LINER" doesn't mean low-level AGN. With very low SFR any old stellar population can and will produce ionisation that will have line ratios fall into the LINER regime. Which is more likely to be seen when doing spatially-resolved IFU spectroscopy:

https://ui.adsabs.harvard.edu/abs/2013A%26A...558A..43S/abstract

Show threadPᵉtɘr Wᵉil8acherApr 17, 2024
@knud The spectrum of that off-center source is actually dominated by emission lines, I don't think old stars could contribute enough flux to that, given the equivalent width. The nucleus itself is different, much stronger continuum (and much further into the LINER regime).
Show threadKnud JahnkeApr 17, 2024

@PWei888

Don't say that - the post-AGB stars have a very hard spectrum. So you will get the corresponding lines. Not very intense, but if you see lines, you will get the lines corresponding to that hard spectrum.

So it hinges on EW, if I remember correctly if Ha has more than 2(?)nm then it's likely not pAGB stars. But if below then it's likely.

Show threadPᵉtɘr Wᵉil8acherApr 17, 2024
@knud I don't have the exact spectrum that Evelyn extracted for the off-centerr source, but the EW is higher than that in my version (more like 80-90Å). Those old stars usually do not generate ionization with emission lines on the star-forming border of the BPT diagram. (The relevant point is the filled black circle in the BPT diagram that I posted, I guess that wasn't clear.) So I guess old stars could contribute but do not dominate the emission.
Show threadKnud JahnkeApr 18, 2024

@PWei888

I was mostly referring to the small blue points, which could be a mix of LINER and SF, the black point is indeed very different.