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MHONGOOSE discovery of a gas-rich low-surface brightness galaxy in the Dorado Group
F. M. Maccagni, W. J. G. de Blok, P. E. Mancera Piña, R. Ragusa, E. Iodice, M. Spavone, S. McGaugh, K. A. Oman, T. A. Oosterloo, B. S. Koribalski, M. Kim, E. A. K. Adams, P. Amram, A. Bosma, F. Bigiel, E. Brinks, L. Chemin, F. Combes, B. Gibson, J. Healy, et al (11)
May 28 2024 astro-ph.GA arXiv:2405.17000v1

@misc{2405.17000, author = {F.~M.~Maccagni and W.~J.~G.~de Blok and P.~E.~Mancera Piña and R.~Ragusa and E.~Iodice and M.~Spavone and S.~McGaugh and K.~A.~Oman and T.~A.~Oosterloo and B.~S.~Koribalski and M.~Kim and E.~A.~K.~Adams and P.~Amram and A.~Bosma and F.~Bigiel and E.~Brinks and L.~Chemin and F.~Combes and B.~Gibson and J.~Healy and B.~W.~Holwerda and G.~I.~G.~Józsa and P.~Kamphuis and D.~Kleiner and S.~Kurapati and A.~Marasco and K.~Spekkens and S.~Veronese and F.~Walter and N.~Zabel and A.~Zijlstra}, title = {{MHONGOOSE} discovery of a gas-rich low-surface brightness galaxy in the {D}orado {G}roup}, year = {2024}, eprint = {2405.17000}, note = {arXiv:2405.17000v1} }
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We present the discovery of a low-mass gas-rich low-surface brightness galaxy in the Dorado Group, at a distance of 17.7 Mpc. Combining deep MeerKAT 21-cm observations from the MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey with deep photometric images from the VST Early-type Galaxy Survey (VEGAS) we find a stellar and neutral atomic hydrogen (HI) gas mass of $M_\star = 2.23\times10^6$ M$_\odot$ and $M_{\rm HI}=1.68\times10^6$ M$_\odot$, respectively. This low-surface brightness galaxy is the lowest mass HI detection found in a group beyond the Local Universe ($D\gtrsim 10$ Mpc). The dwarf galaxy has the typical overall properties of gas-rich low surface brightness galaxies in the Local group, but with some striking differences. Namely, the MHONGOOSE observations reveal a very low column density ($\sim 10^{18-19}$ cm$^{-2}$) HI disk with asymmetrical morphology possibly supported by rotation and higher velocity dispersion in the centre. There, deep optical photometry and UV-observations suggest a recent enhancement of the star formation. Found at galactocentric distances where in the Local Group dwarf galaxies are depleted of cold gas (at $390$ projected-kpc distance from the group centre), this galaxy is likely on its first orbit within the Dorado group. We discuss the possible environmental effects that may have caused the formation of the HI disk and the enhancement of star formation, highlighting the short-lived phase (a few hundreds of Myr) of the gaseous disk, before either SF or hydrodynamical forces will deplete the gas of the galaxy.
MHONGOOSE -- A MeerKAT Nearby Galaxy HI Survey
W.J.G. de Blok, J. Healy, F.M. Maccagni, D.J. Pisano, A. Bosma, J. English, T. Jarrett, A. Marasco, G.R. Meurer, S. Veronese, F. Bigiel, L. Chemin, F. Fraternali, B.W. Holwerda, P. Kamphuis, H.R. Klöckner, D. Kleiner, A.K. Leroy, M. Mogotsi, K.A. Oman, et al (40)
Apr 03 2024 astro-ph.GA arXiv:2404.01774v2

@misc{2404.01774, author = {W.J.G.~de Blok and J.~Healy and F.M.~Maccagni and D.J.~Pisano and A.~Bosma and J.~English and T.~Jarrett and A.~Marasco and G.R.~Meurer and S.~Veronese and F.~Bigiel and L.~Chemin and F.~Fraternali and B.W.~Holwerda and P.~Kamphuis and H.R.~Klöckner and D.~Kleiner and A.K.~Leroy and M.~Mogotsi and K.A.~Oman and E.~Schinnerer and L.~Verdes-Montenegro and T.~Westmeier and O.I.~Wong and N.~Zabel and P.~Amram and C.~Carignan and F.~Combes and E.~Brinks and R.J.~Dettmar and B.K.~Gibson and G.I.G.~Jozsa and B.S.~Koribalski and S.S.~McGaugh and T.A.~Oosterloo and K.~Spekkens and A.C.~Schröder and E.A.K.~Adams and E.~Athanassoula and M.A.~Bershady and R.J.~Beswick and S.~Blyth and E.C.~Elson and B.S.~Frank and G.~Heald and P.A.~Henning and S.~Kurapati and S.I.~Loubser and D.~Lucero and M.~Meyer and B.~Namumba and S.-H.~Oh and A.~Sardone and K.~Sheth and M.W.L.~Smith and A.~Sorgho and F.~Walter and T.~Williams and P.A.~Woudt and A.~Zijlstra}, title = {{MHONGOOSE} -- {A} {M}eer{KAT} {N}earby {G}alaxy {HI} {S}urvey}, year = {2024}, eprint = {2404.01774}, note = {arXiv:2404.01774v2} }
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The MHONGOOSE (MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters) survey maps the distribution and kinematics of the neutral atomic hydrogen (HI) gas in and around 30 nearby star-forming spiral and dwarf galaxies to extremely low HI column densities. The HI column density sensitivity (3 sigma over 16 km/s) ranges from ~ 5 x 10^17 cm^-2 at 90'' resolution to ~4 x 10^19 cm^-2 at the highest resolution of 7''. The HI mass sensitivity (3 sigma over 50 km/s) is ~5.5 X 10^5 M_sun at a distance of 10 Mpc (the median distance of the sample galaxies). The velocity resolution of the data is 1.4 km/s. One of the main science goals of the survey is the detection of cold, accreting gas in the outskirts of the sample galaxies. The sample was selected to cover a range in HI masses, from 10^7 M_sun to almost 10^11 M_sun, to optimally sample possible accretion scenarios and environments. The distance to the sample galaxies ranges from 3 to 23 Mpc. In this paper, we present the sample selection, survey design, and observation and reduction procedures. We compare the integrated HI fluxes based on the MeerKAT data with those derived from single-dish measurement and find good agreement, indicating that our MeerKAT observations are recovering all flux. We present HI moment maps of the entire sample based on the first ten percent of the survey data, and find that a comparison of the zeroth- and second-moment values shows a clear separation between the physical properties of the HI in areas with star formation and areas without, related to the formation of a cold neutral medium. Finally, we give an overview of the HI-detected companion and satellite galaxies in the 30 fields, five of which have not previously been catalogued. We find a clear relation between the number of companion galaxies and the mass of the main target galaxy.
Possible origins of anomalous H$\,$I gas around MHONGOOSE galaxy, NGC 5068
J. Healy, W.J.G. de Blok, F.M. Maccagni, P. Amram, L. Chemin, F. Combes, B.W. Holwerda, P. Kamphuis, D.J. Pisano, E. Schinnerer, K. Spekkens, L. Verdes-Montenegro, F. Walter, E.A.K. Adams, B.K. Gibson, D. Kleiner, S. Veronese, N. Zabel, J. English, C. Carignan
Feb 22 2024 astro-ph.GA arXiv:2402.13749v1

@misc{2402.13749, author = {J.~Healy and W.J.G.~de Blok and F.M.~Maccagni and P.~Amram and L.~Chemin and F.~Combes and B.W.~Holwerda and P.~Kamphuis and D.J.~Pisano and E.~Schinnerer and K.~Spekkens and L.~Verdes-Montenegro and F.~Walter and E.A.K.~Adams and B.K.~Gibson and D.~Kleiner and S.~Veronese and N.~Zabel and J.~English and C.~Carignan}, title = {{P}ossible origins of anomalous {H}$\,${I} gas around {MHONGOOSE} galaxy, {NGC} 5068}, year = {2024}, eprint = {2402.13749}, note = {arXiv:2402.13749v1} }
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The existing reservoirs of neutral atomic hydrogen gas (H$\,$I) in galaxies are insufficient to have maintained the observed levels of star formation without some kind of replenishment. This refuelling of the H$\,$I reservoirs is likely to occur at column densities an order of magnitude lower than previous observational limits (N$_{\rm{H\,I}\, limit} \sim 10^{19}\,$cm$^{-2}$ at 30$''$ resolution over a linewidth of $20\,$km/s). In this paper, we present recent deep H$\,$I observations of NGC 5068, a nearby isolated star-forming galaxy observed by MeerKAT as part of the MHONGOOSE survey. With these new data, we are able to detect low column density H$\,$I around NGC 5068 with a $3\sigma$ detection limit of N$_{\rm{H\,I}} = 6.4 \times 10^{17}\,$cm$^{-2}$ at 90$''$ resolution over a $20\,$km/s linewidth. The high sensitivity and resolution of the MeerKAT data reveal a complex morphology of the H$\,$I in this galaxy -- a regularly rotating inner disk coincident with the main star-forming disk of the galaxy, a warped outer disk of low column density gas (N$_{\rm{H\,I}} < 9 \times 10^{19}\,$cm$^{-2}$), in addition to clumps of gas on the north west side of the galaxy. We employ a simple two disk model that describe the inner and outer disks, and are able to identify anomalous gas that deviates from the rotation of the main galaxy. The morphology and the kinematics of the anomalous gas suggest a possible extra-galactic origin. We explore a number of possible origin scenarios that may explain the anomalous gas, and conclude that fresh accretion is the most likely scenario.
Interpreting the long-term variability of the changing-look AGN Mrk 1018
S. Veronese, C. Vignali, P. Severgnini, G. A. Matzeu, M. Cignoni
Dec 14 2023 astro-ph.HE astro-ph.GA arXiv:2312.07663v1

@misc{2312.07663, author = {S.~Veronese and C.~Vignali and P.~Severgnini and G.~A.~Matzeu and M.~Cignoni}, title = {{I}nterpreting the long-term variability of the changing-look {AGN} {M}rk 1018}, year = {2023}, eprint = {2312.07663}, note = {arXiv:2312.07663v1} }
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We present a thorough study of the Changing-Look Active Galactic Nucleus (CL-AGN) Mrk 1018, utilizing an extensive dataset spanning optical, UV, and X-ray spectro-photometric data from 2005 to 2019. We analysed X-ray spectra and broad-band photometry, and performed optical-to-X-ray spectral energy distribution (SED) fitting to comprehend the observed changing-look behaviour. We found that over the 14 years in analysis, significant changes in X-ray spectra occurred, as the hardness ratio increases by a factor of ~2. We validated also the broad-band dimming, with optical, UV, and X-ray luminosities decreasing by factors of >7, >24 and ~9, respectively. These dims are attributed to the declining UV emission. We described the X-ray spectra with a two-Comptonization model, revealing a consistent hot comptonizing medium but a cooling warm component. This cooling, linked to the weakening of the magnetic fields in the accretion disk, explains the UV dimming. We propose that the weakening is caused by the formation of a jet, in turn originated from the change of state of the inner accretion flow. Our optical-to-X-ray SED fitting supports this conclusion, as the normalised accretion rate is super-critical ($\mu=$0.06>0.02) in the bright state and sub-critical ($\mu=$0.01<0.02) in the faint state. Instabilities arising at the interface of the state-transition are able to reduce the viscous timescale to the observed ~10 years of Mrk 1018 variability. We explored a possible triggering mechanism for this state transition, involving gaseous clouds pushed onto the AGN sub-pc regions by a recent merging event or by cold chaotic accretion. This scenario, if validated by future simulations, could enhance our understanding of CL-AGN and raises questions about an accretion rate of ~0.02, coupled with minor disturbances in the accretion disk, being the primary factor in the changing-look phenomenon.
Extended neutral hydrogen filamentary network in NGC 2403
S. Veronese, W. J. G. de Blok, F. Walter
Feb 01 2023 astro-ph.GA arXiv:2301.13526v1

@misc{2301.13526, author = {S.~Veronese and W.~J.~G.~de Blok and F.~Walter}, title = {{E}xtended neutral hydrogen filamentary network in {NGC} 2403}, year = {2023}, eprint = {2301.13526}, note = {arXiv:2301.13526v1} }
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We present new neutral hydrogen (HI) observations of the nearby galaxy NGC 2403 to determine the nature of a low-column density cloud that was detected earlier by the Green Bank Telescope. We find that this cloud is the tip of a complex of filaments of extraplanar gas that is coincident with the thin disk. The total HI mass of the complex is $2\times10^{7}\text{ M}_\odot$ or 0.6% of the total HI mass of the galaxy. The main structure, previously referred to as the 8-kpc filament, is now seen to be even more extended, along a 20 kpc stream. The kinematics and morphological properties of the filaments are unlikely to be the result of outflows related to galactic fountains. It is more likely that the 20 kpc filament is related to a recent galaxy interaction. In this context, a $\sim$ 50 kpc long stellar stream has been recently detected connecting NGC 2403 with the nearby dwarf satellite DDO 44. Intriguingly, the southern tip of this stream overlaps with that of 20 kpc HI filament. We conclude that the HII anomalies in NGC 2403 are the result of a recent ($\sim2\text{ Gyr}$) interaction with DDO 44 leading to the observed filamentary complex.