Browsing by Author "Nagar, N."

Now showing 1 - 5 of 5
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    Detailed Accretion History of the Supermassive Black Hole in NGC 5972 over the Past ≳104 yr through the Extended Emission-line Region
    (2022) Finlez, C.; Treister, E.; Bauer, F.; Keel, W.; Koss, M.; Nagar, N.; Sartori, L.; Maksym, W. P.; Venturi, G.; Tubin, D.; Harvey, T.
    We present integral field spectroscopic observations of NGC 5972 obtained with the Multi-Unit Spectroscopic Explorer at the Very Large Telescope. NGC 5972 is a nearby galaxy containing both an active galactic nucleus (AGN) and an extended emission-line region (EELR) reaching out to similar to 17 kpc from the nucleus. We analyze the physical conditions of the EELR using spatially resolved spectra, focusing on the radial dependence of ionization state together with the light-travel time distance to probe the variability of the AGN on greater than or similar to 10(4) yr timescales. The kinematic analysis suggests multiple components: (a) a faint component following the rotation of the large-scale disk, (b) a component associated with the EELR suggestive of extraplanar gas connected to tidal tails, and (c) a kinematically decoupled nuclear disk. Both the kinematics and the observed tidal tails suggest a major past interaction event. Emission-line diagnostics along the EELR arms typically evidence Seyfert-like emission, implying that the EELR was primarily ionized by the AGN. We generate a set of photoionization models and fit these to different regions along the EELR. This allows us to estimate the bolometric luminosity required at different radii to excite the gas to the observed state. Our results suggest that NGC 5972 is a fading quasar, showing a steady gradual decrease in intrinsic AGN luminosity, and hence the accretion rate onto the SMBH, by a factor similar to 100 over the past 5 x 10(4) yr.
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    The ALMA Frontier Fields Survey IV. Lensing-corrected 1.1 mm number counts in Abell 2744, MACS J0416.1-2403 and MACS J1149.5+2223
    (2018) Munoz Arancibia, A.M.; González López, Jorge; Ibar, E.; Bauer, Franz Erik; Carrasco, M.; Laporte, L.N.; Anguita, T.; Aravena, M.; Infante Lira, Leopoldo; Padilla, Nelson; Barrientos, Andrés F.; Bouwens, R.J.; Demarco, R.; Kneiss, R.; Nagar, N.; Romero-Cañizales, C.; Troncoso, P.; A. Zitrin
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    The ALMA Frontier Fields Survey. IV. Lensing-corrected 1.1 mm number counts in Abell 2744, MACS J0416.1-2403, and MACS J1149.5+2223 (Corrigendum)
    (2019) Muñoz Arancibia, A. M.; González-López, J.; Ibar, E.; Bauer, F. E.; Carrasco, M.; Laporte, N.; Anguita, T.; Aravena, M.; Barrientos, F.; Bouwens, R. J.; Demarco, R.; Infante, L.; Kneissl, R.; Nagar, N.; Padilla, N.; Romero-Cañizales, C.; Troncoso, P.; Zitrin, A.
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    The hidden side of cosmic star formation at z > 3 Bridging optically dark and Lyman-break galaxies with GOODS-ALMA
    (2023) Xiao, M-Y.; Elbaz, D.; Gomez-Guijarro, C.; Leroy, L.; Bing, L-J.; Daddi, E.; Magnelli, B.; Franco, M.; Zhou, L.; Dickinson, M.; Wang, T.; Rujopakarn, W.; Magdis, G. E.; Treister, Ezequiel; Inami, H.; Demarco, R.; Sargent, M. T.; Shu, X.; Kartaltepe, J. S.; Alexander, D. M.; Bethermin, M.; Bournaud, F.; Ciesla, L.; Ferguson, H. C.; Finkelstein, S. L.; Giavalisco, M.; Gu, Q-S.; Iono, D.; Juneau, S.; Lagache, G.; Leiton, R.; Messias, H.; Motohara, K.; Mullaney, J.; Nagar, N.; Pannella, M.; Papovich, C.; Pope, A.; Schreiber, C.; Silverman, J.
    Our current understanding of the cosmic star formation history at z > 3 is primarily based on UV-selected galaxies (Lyman-break galaxies, i.e., LBGs). Recent studies of H-dropouts (HST-dark galaxies) have revealed that we may be missing a large proportion of star formation that is taking place in massive galaxies at z > 3. In this work, we extend the H-dropout criterion to lower masses to select optically dark or faint galaxies (OFGs) at high redshifts in order to complete the census between LBGs and H-dropouts. Our criterion (H > 26.5 mag & [4.5] < 25 mag) combined with a de-blending technique is designed to select not only extremely dust-obscured massive galaxies but also normal star-forming galaxies (typically E(B - V) > 0.4) with lower stellar masses at high redshifts. In addition, with this criterion, our sample is not contaminated by massive passive or old galaxies. In total, we identified 27 OFGs at (Zphot) > 3 (with a median of z(med) = 4.1) in the GOODS-ALMA field, covering a wide distribution of stellar masses with log(M-star/M-circle dot) = 9.4-11.1 (with a median of log(M-star med/M-circle dot) = 10.3). We find that up to 75% of the OFGs with log(M-star/M-circle dot) = 9.5-10.5 were neglected by previous LBGs and H-dropout selection techniques. After performing an optical-to-millimeter stacking analysis of the OFGs, we find that rather than being limited to a rare population of extreme starbursts, these OFGs represent a normal population of dusty star-forming galaxies at z > 3. The OFGs exhibit shorter gas depletion timescales, slightly lower gas fractions, and lower dust temperatures than the scaling relation of typical star-forming galaxies. Additionally, the total star formation rate (SFRtot = SFRIR + SFRUV) of the stacked OFGs is much higher than the SFRUVcorr (SFRUV corrected for dust extinction), with an average SFRtot/SFRUVcorr = 8 +/- 1, which lies above (similar to 0.3 dex) the 16-84th percentile range of typical star-forming galaxies at 3 <= z <= 6. All of the above suggests the presence of hidden dust regions in the OFGs that absorb all UV photons, which cannot be reproduced with dust extinction corrections. The effective radius of the average dust size measured by a circular Gaussian model fit in the uv plane is R-e(1.13 mm) = 1.01 +/- 0.05 kpc. After excluding the five LBGs in the OFG sample, we investigated their contributions to the cosmic star formation rate density (SFRD). We found that the SFRD at z > 3 contributed by massive OFGs (log(M-star/M-circle dot) > 10.3) is at least two orders of magnitude higher than the one contributed by equivalently massive LBGs. Finally, we calculated the combined contribution of OFGs and LBGs to the cosmic SFRD at z = 4-5 to be 4 x 10(-2) M-circle dot yr(-1) Mpc(-3), which is about 0.15 dex (43%) higher than the SFRD derived from UV-selected samples alone at the same redshift. This value could be even larger, as our calculations were performed in a very conservative way.
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    The hidden side of cosmic star formation at z > 3 Bridging optically dark and Lyman-break galaxies with GOODS-ALMA
    (Wiley, 2023) Xiao, M-Y.; Elbaz, D.; Gomez-Guijarro, C.; Leroy, L.; Bing, L-J.; Daddi, E.; Magnelli, B.; Franco, M.; Zhou, L.; Dickinson, M.; Wang, T.; Rujopakarn, W.; Magdis, G. E.; Treister, Ezequiel; Inami, H.; Demarco, R.; Sargent, M. T.; Shu, X.; Kartaltepe, J. S.; Alexander, D. M.; Bethermin, M.; Bournaud, F.; Ciesla, L.; Ferguson, H. C.; Finkelstein, S. L.; Giavalisco, M.; Gu, Q-S.; Iono, D.; Juneau, S.; Lagache, G.; Leiton, R.; Messias, H.; Motohara, K.; Mullaney, J.; Nagar, N.; Pannella, M.; Papovich, C.; Pope, A.; Schreiber, C.; Silverman, J.
    Our current understanding of the cosmic star formation history at z > 3 is primarily based on UV-selected galaxies (Lyman-break galaxies, i.e., LBGs). Recent studies of H-dropouts (HST-dark galaxies) have revealed that we may be missing a large proportion of star formation that is taking place in massive galaxies at z > 3. In this work, we extend the H-dropout criterion to lower masses to select optically dark or faint galaxies (OFGs) at high redshifts in order to complete the census between LBGs and H-dropouts. Our criterion (H > 26.5 mag & [4.5] < 25 mag) combined with a de-blending technique is designed to select not only extremely dust-obscured massive galaxies but also normal star-forming galaxies (typically E(B - V) > 0.4) with lower stellar masses at high redshifts. In addition, with this criterion, our sample is not contaminated by massive passive or old galaxies. In total, we identified 27 OFGs at (Zphot) > 3 (with a median of z(med) = 4.1) in the GOODS-ALMA field, covering a wide distribution of stellar masses with log(M-star/M-circle dot) = 9.4-11.1 (with a median of log(M-star med/M-circle dot) = 10.3). We find that up to 75% of the OFGs with log(M-star/M-circle dot) = 9.5-10.5 were neglected by previous LBGs and H-dropout selection techniques. After performing an optical-to-millimeter stacking analysis of the OFGs, we find that rather than being limited to a rare population of extreme starbursts, these OFGs represent a normal population of dusty star-forming galaxies at z > 3. The OFGs exhibit shorter gas depletion timescales, slightly lower gas fractions, and lower dust temperatures than the scaling relation of typical star-forming galaxies. Additionally, the total star formation rate (SFRtot = SFRIR + SFRUV) of the stacked OFGs is much higher than the SFRUVcorr (SFRUV corrected for dust extinction), with an average SFRtot/SFRUVcorr = 8 +/- 1, which lies above (similar to 0.3 dex) the 16-84th percentile range of typical star-forming galaxies at 3 <= z <= 6. All of the above suggests the presence of hidden dust regions in the OFGs that absorb all UV photons, which cannot be reproduced with dust extinction corrections. The effective radius of the average dust size measured by a circular Gaussian model fit in the uv plane is R-e(1.13 mm) = 1.01 +/- 0.05 kpc. After excluding the five LBGs in the OFG sample, we investigated their contributions to the cosmic star formation rate density (SFRD). We found that the SFRD at z > 3 contributed by massive OFGs (log(M-star/M-circle dot) > 10.3) is at least two orders of magnitude higher than the one contributed by equivalently massive LBGs. Finally, we calculated the combined contribution of OFGs and LBGs to the cosmic SFRD at z = 4-5 to be 4 x 10(-2) M-circle dot yr(-1) Mpc(-3), which is about 0.15 dex (43%) higher than the SFRD derived from UV-selected samples alone at the same redshift. This value could be even larger, as our calculations were performed in a very conservative way.