Contact:
STScI
3700 San Martin Dr
Baltimore, MD 21210, USA
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Research Interests:
Epoch of Reionization
High redshift galaxies and their local analogues, star-forming galaxies, emission line galaxies
Star-forming regions, diffuse ionised gas, compact high-velocity clouds
Physics of the interstellar medium, chemical abundances, metallicity gradients
Metallicity scaling relations, Metallicity diagnostics, Schmidt relation of star-formation
Research Highlights
A study of extreme C III]1908 & [O III]88/[C II]157 emission in Pox 186: implications for JWST+ALMA (FUV + FIR) studies of distant galaxies
In Kumari+2024, we performed a multi-wavelength of Pox 186, potentially the best local analogue of reionization era galaxies as evidenced by the extreme FIR [OIII]88/[CII]157 line ratio (~10), and equivalent width of UV CIII] line (~35 Angstrom). Both C III] and C IV line profiles are broadened with respect to the O III] λ1666 emission line. Each emission line of C IV λλ1548, 1550 shows the most distinct double-peak structure detected so far. The study demonstrates that galaxies with extreme FIR properties may also show extreme UV properties, hence paving a promising avenue of using FIR+UV in the local (via Hubble+Herschel/SOFIA) and distant (via JWST + ALMA) Universe for unveiling the mysteries of the reionization-era.
EW(CIII]) versus EW([OIII]+Hbeta) for Pox 186 (red dot) & galaxies at various redshifts taken from literature (Kumari+2024, Figure 6)
Evidence of infall and starvation in the FMR extension to BPT-non-SF galaxies (Kumari+2021b, Figure 4)
Extension of FMR to galaxies beyond the star-forming sequence on the BPT diagram: evidence of gas-infall and starvation
In Kumari+2021b, we extended the fundamental metallicity relation (FMR) to the BPT-non-SF galaxies, i.e. galaxies lying beyond the maximum starburst line on the classical emission line diagnostic diagram.
We find that galaxies with SFR higher than the Main Sequence (MS) are more metal-poor than their counterparts on the MS, which is interpreted in terms of gas accretion, boosting star formation and diluting the metallicity. Low-mass galaxies below the MS (i.e. towards quiescence) have metallicities higher than their MS counterparts, which is interpreted in terms of starvation, (i.e. suppression of fresh gas supply) hampering star formation and reducing the dilution eect, hence resulting in a higher level of internal chemical enrichment. Massive galaxies below the MS have gas metallicity much closer to their MS counterparts and much lower than expected from their stellar metallicities; this result suggests a scenario where massive nearly-quiescent galaxies with LI(N)ER-like nebular emission have recently accreted gas from the circum/intergalactic medium.
Hardness of ionizing radiation fields using MaNGA star-forming galaxies
In Kumari+2021a, we explored radiation hardness within a representative sample of 67 MaNGA galaxies via observational softness parameter \eta'. We found that low-metallicity is accompanied by harder radiation field. We provide empirical relations to estimate softness parameter from strong-line ratios, such as O3N2, N2 and Ar3O3 for galaxies/HII regions with sub-solar metallicity (7.12 < 12+log(O/H) < 8.6).
We found that photoionization models (3mDB) containing both young and old stellar populations are required to explain the observed \eta values in our MaNGA data.
Empirical calibration to estimate softness parameter \eta from N2 line ratio (Kumari+2021, Figure 6)
Agreement of global and local Schmidt relation after subtraction of diffuse background (Kumari+2020, Figure 9).
Agreement between Local and Global Schmidt relation of Star-formation:
In Kumari+2020, we showed that subtraction of diffuse background in SFR tracers and atomic gas lead to a slope of ~1.4 +/- 0.1 in Schmidt relation of star-formation, and agrees global Schmidt relation along with dynamical models of star formation (Elmegreen+2015) accounting for flaring effects in the outer regions of galaxies.
For this work, we used muliwavelength dataset (FUV, Ha, IR, HI, CO) from different surveys and software Nebuliser to remove underlying background.
First metallicity calibrations for Diffuse Ionized Gas and Low-Ionization Emission Regions:
In Kumari+2019a, we derived the first ever metallicity calibrations based on O3N2 and O3S2 diagnostics for diffuse ionized gas and low-ionization emission regions, which will allow us to constrain gas-phase metallicity of quiscent galaxies or in quiscent regions of star-forming galaxies.
Derivation of first metallicity calibration for DIG (Kumari+2019a,Figure 8).
Chemical homogeneity within a GMOS-FOV containing several HII regions (Kumari+2019b, Figure 15).
More robust tests of Chemical Homogeneity needed:
In Kumari+2019b, we derived ionic and elemental abundances of several elements and studied chemical variation within concentric ellipitcal regions. We found that no chemical variation even though the studied region of SBS1415+437 contains several HII regions. This study shows that the tests of chemical homogeneity must account for both the spatial information as well as the spaxel error, and we also need to consider the effects of seeing which tends to wash out small spatial scale variation in the abundance maps.
O/H-N/O: the curious case of NGC 4670:
In Kumari+2018, we find an unexpected negative trend between N/O and gas-phase metallicity within a blue compact dwarf galaxy NGC 4670. Several scenarios are explored to explain this trend, including local nitrogen enrichment (probably due to Wolf-Rayet stars), and variations in star formation efficiency via chemical evolution models (Vincenzo+2018).
Unusual negative trend b/w N/O and O/H found within NGC 4670 (Kumari+2018, Figure 22).
Inverse metallicity gradient within NGC 4449 (Kumari+2017, Figure 19).
Metal-poor centre of NGC 4449:
In Kumari+2017, we find evidence of inverse metallicity gradient within NGC 4449. Such chemical inhomogeneities can be due to several mechanisms, including gas loss via supernova blowout, galactic winds or metal-poor gas accretion. However, we find that the localized area of decreased metallicity aligns spatially with the peak of star-forming activity in the galaxy, suggesting that gas accretion may be at play here.
Origin of CHVC in the Magellanic Stream:
In Kumari+2015, we find that the compact high velcoity cloud (CHVC) under study has metal abundance of 0.1 solar which matches the abundance measured along the main body of the Magellanic Stream, suggesting that the CHVC has its origin in the Stream. This is reinforced by the similar central velocity of the CHVC and the Stream in this part of the sky. The CHVC may represent a fragment of the Stream that has been removed by its interaction with the surrounding plasma.
CHVC metal abundance of 0.1 solar matches that of the main body of Magellanic stream (Kumari+2015, Figure 11).
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