Revisiting the Group-Dominant Elliptical NGC 5044 in the Radio Band: Continuum Emission and Detection of HI Absorption
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| Natura: | Preprint |
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2025
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| author | Rajpurohit, Kamlesh Deb, Tirna Kolokythas, Konstantinos Thorat, Kshitij O'Sullivan, Ewan Schellenberger, Gerrit David, Laurence P. Vrtilek, Jan M. Giacintucci, Simona Forman, William Jones, Christine Ramatsoku, Mpati |
| author_facet | Rajpurohit, Kamlesh Deb, Tirna Kolokythas, Konstantinos Thorat, Kshitij O'Sullivan, Ewan Schellenberger, Gerrit David, Laurence P. Vrtilek, Jan M. Giacintucci, Simona Forman, William Jones, Christine Ramatsoku, Mpati |
| contents | We present new MeerKAT L-band (continuum and HI) and upgraded Giant Metrewave Radio Telescope (300-850 MHz) observations of the archetypal cool-core group-dominant early-type galaxy NGC 5044. Our new continuum images reveal diffuse, steep spectrum ($α_{0.99\,\rm GHz}^{1.56\,\rm GHz}=-1.53\pm0.6$) radio emission extending about 25 kpc around the unresolved radio core. The observed radio emission overlaps with the known X-ray cavities, but is not confined to them. We also find the first direct evidence of neutral atomic gas in NGC 5044, in the form of a 3.8$σ$ significant two-component HI absorption line seen against the emission of the active nucleus. The peak velocities are well correlated with the previously reported CO(2-1) absorption, but the HI lines are moderately broader, spanning velocities from $265\,\rm \, km\,s^{-1}$ to $305\,\rm \, km\,s^{-1}$. We do not detect HI emission, but place an upper limit of $M_{HI}< 5.4 \times 10^{7} \, M_{\odot}$ in the central 15 arcsec (2.2 kpc) of the galaxy. This is significantly less than the estimated molecular gas content, and implies a molecular-to-atomic mass ratio of $\geq $1.7:1, consistent with these gas phases forming through cooling from the hot intra-group medium. We also constrain the spin temperature to $T_{\rm spin}\leq 950\,\rm K$, indicating that the detected HI is in the cold neutral phase. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2501_02076 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Revisiting the Group-Dominant Elliptical NGC 5044 in the Radio Band: Continuum Emission and Detection of HI Absorption Rajpurohit, Kamlesh Deb, Tirna Kolokythas, Konstantinos Thorat, Kshitij O'Sullivan, Ewan Schellenberger, Gerrit David, Laurence P. Vrtilek, Jan M. Giacintucci, Simona Forman, William Jones, Christine Ramatsoku, Mpati Astrophysics of Galaxies We present new MeerKAT L-band (continuum and HI) and upgraded Giant Metrewave Radio Telescope (300-850 MHz) observations of the archetypal cool-core group-dominant early-type galaxy NGC 5044. Our new continuum images reveal diffuse, steep spectrum ($α_{0.99\,\rm GHz}^{1.56\,\rm GHz}=-1.53\pm0.6$) radio emission extending about 25 kpc around the unresolved radio core. The observed radio emission overlaps with the known X-ray cavities, but is not confined to them. We also find the first direct evidence of neutral atomic gas in NGC 5044, in the form of a 3.8$σ$ significant two-component HI absorption line seen against the emission of the active nucleus. The peak velocities are well correlated with the previously reported CO(2-1) absorption, but the HI lines are moderately broader, spanning velocities from $265\,\rm \, km\,s^{-1}$ to $305\,\rm \, km\,s^{-1}$. We do not detect HI emission, but place an upper limit of $M_{HI}< 5.4 \times 10^{7} \, M_{\odot}$ in the central 15 arcsec (2.2 kpc) of the galaxy. This is significantly less than the estimated molecular gas content, and implies a molecular-to-atomic mass ratio of $\geq $1.7:1, consistent with these gas phases forming through cooling from the hot intra-group medium. We also constrain the spin temperature to $T_{\rm spin}\leq 950\,\rm K$, indicating that the detected HI is in the cold neutral phase. |
| title | Revisiting the Group-Dominant Elliptical NGC 5044 in the Radio Band: Continuum Emission and Detection of HI Absorption |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2501.02076 |