Chemical signatures of a prestellar cluster in the Galactic Center
Abstract
The Central Molecular Zone (CMZ) contains most of the mass of our Galaxy, but its star formation rate is one order of magnitude lower than in the Galactic disk. This is likely related to the fact that the bulk of the gas in the CMZ is in a warm (100 K) and turbulent phase with little material in the prestellar phase. I will present D/H ratios of HCN, HNC, HCO+, and N2H+ obtained towards the CMZ molecular cloud G+0.693-0.027 (Colzi et al. 2022). These observations clearly show, for the first time, the presence of a colder, denser and narrow component, with a line width of about 9 km s-1, in addition to the warm, less dense, and turbulent broad component with a line width of about 20 km s-1. For this new component D/H ratios higher than 1e-4 and excitation temperatures of 7 K for all molecules have been found, suggesting kinetic temperatures lower than 30 K and H2 densities higher than 5e4 cm-3. This new method indicates that the degree of deuteration of different molecules, such as N2H+ and HCO+, and their line profiles, can be used to reveal the different gas components in the line of sight to the CMZ. Then, I will present HC3N excitation-derived gas densities and temperatures of the gas components towards the same source, using multiple transitions coupled with spatially resolved HC3N images of the source. This approach allows us to identify denser gas that possibly is on the verge of gravitational collapse and that will host future protostars in the CMZ (Colzi et al. 2024).
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Chemical Signatures of a prestellar cluster in the Galactic Center Laura Colzi (Centro de Astrobiología, CSIC-INTA) March 10th 2025 J. Martín-Pintado, S. Zeng, I. Jiménez-Serra,V. M. Rivilla, Sanz-Novo, M. and many others... Grant PID2022-136814NB-I00 funded by:
Herschel PACS 70 µm image of the Galactic center region. Molinari et al. (2001) The CMZ contains 80% of the dense molecular gas in the Galaxy BUT the recent star formation rate is one order of magnitude lower than that in the disk (e.g. Longmore et al. 2013; Barnes et al. 2017)
ØHigh level of turbulence due to the large internal cloud velocity dispersion (∼15–50 km s−1) AND ØWidespread high kinetic temperatures (Tkin from ∼50 K to >100 K) EXTREME ENVIRONMENTAL CONDITIONS could prevent star formation Image Credit: radio image from MeerKAT. Ian Heywood (Oxford U.), SARAO; Color Processing: Juan Carlos Munoz-Mateos (ESO)
ØHigh level of turbulence due to the large internal cloud velocity dispersion (∼15–50 km s−1) AND ØWidespread high kinetic temperatures (Tkin from ∼50 K to >100 K) EXTREME ENVIRONMENTAL CONDITIONS could prevent star formation BUT do not stop it entirely à Sgr B2 and Sgr C, Arches, Quintuplet, the Brick (e.g. Longmore+2013b; Walker+2021) Image Credit: radio image from MeerKAT. Ian Heywood (Oxford U.), SARAO; Color Processing: Juan Carlos Munoz-Mateos (ESO)
Image Credit: radio image from MeerKAT. Ian Heywood (Oxford U.), SARAO; Color Processing: Juan Carlos Munoz-Mateos (ESO) ØLarge column densities of warm and turbulent gas Moreover… àDifficult to disentangle signatures of denser and less turbulent prestellar cores
Image Credit: radio image from MeerKAT. Ian Heywood (Oxford U.), SARAO; Color Processing: Juan Carlos Munoz-Mateos (ESO) ØLarge column densities of warm and turbulent gas Moreover… àDifficult to disentangle signatures of denser and less turbulent prestellar cores HOW to identify and study the earlier evolutionary stages of the dense, cold, and quiescent prestellar cores, if present?
Herschel PACS 70 µm image of the Galactic center region. Molinari et al. (2001)
Laura Colzi A CMZ SOURCE: G+0.693-0.027
Laura Colzi A CMZ SOURCE: G+0.693-0.027 Arnaud Belloche’s talk tomorrow
Laura Colzi A CMZ SOURCE: G+0.693-0.027
Colzi et al. (2022a), ApJL, 926, L22Laura Colzi Objective à D/H ratios of HCN, HNC, HCO+ and N2H+ Approach à Use of multiple rotational transitions
Colzi et al. (2022a), ApJL, 926, L22Laura Colzi Objective à D/H ratios of HCN, HNC, HCO+ and N2H+ Approach à Use of multiple rotational transitions Discover à 2 line components needed
Colzi et al. (2022a), ApJL, 926, L22 Presence of two different line components: 1. Turbulent (FWHM = 20 km s-1) component (Tex=7 K) Typical of the CMZ 2. Less turbulent (FWHM = 9 km s-1) component (Tex=3-4 K) à Very clear from high-J transitions Laura Colzi Vrad (km s-1)Vrad (km s-1) Ta* (K) Ta* (K)
BROAD COMPONENT NARROW COMPONENT COSMIC D/H = 2.55 x 10-5 1. D/H[HCN, HNC] > cosmic D/H D/H[HCO+, N2H+] à cosmic D/H 2. D/H[HCN, HNC, HCO+, N2H+] > cosmic D/H Colzi et al. (2022), ApJL, 926, L22Laura Colzi DEUTERIUM FRACTIONATION
Laura Colzi Low-temperature Isotopic-exchange reactions GAS-PHASE Colzi et al. (2022), ApJL, 926, L22 H3++ HDH2D++ H2+ 232 K CH3++ H D CH2 D ++ H2+654 K C2H2++ H D C2H D ++ H2+ 550 K Ø for T≤30 K: D/H of N2H+, HCN, HNC, HCO+ enhanced Ø for T>70-80 K: D/H of HCN and HNC enhanced (Roueff+2007, Roueff+2013) for typical n of CMZ (~103-105cm-3, e.g. Ginsburg+2016) e.g. Herbst (2003), Roueff et al. (2013) DEUTERIUM FRACTIONATION T ≤30 K à T > 70 K à
BROAD COMPONENT NARROW COMPONENT COSMIC D/H = 2.55 x 10-5 1. D/H[HCN, HNC] > cosmic D/H D/H[HCO+, N2H+] à cosmic D/H Consistent with T>70 K 2. D/H[HCN, HNC, HCO+, N2H+] > cosmic D/H Colzi et al. (2022), ApJL, 926, L22Laura Colzi Temperature ≤30 K for the narrow component DEUTERIUM FRACTIONATION
Colzi et al. (2022a), ApJL, 926, L22 Presence of two different line components: 1. Turbulent (FWHM = 20 km s-1), warm (Tkin~100 K) and less dense (n ⋆ ~0.3-3x104 cm-3) component Gas component typical of the CMZ ⋆"from non-LTE analysis (RADEX, van der Tak+2007) Laura Colzi Vrad (km s-1)Vrad (km s-1) Ta* (K) Ta* (K) NON-LTE analysis
Colzi et al. (2022a), ApJL, 926, L22 Presence of two different line components: 1. Turbulent (FWHM = 20 km s-1), warm (Tkin~100 K) and less dense (n ⋆ ~0.3-3x104 cm-3) component Gas component typical of the CMZ 2. Less turbulent (FWHM = 9 km s-1), colder (Tkin~20-30 K) and denser component (n ⋆" ~0.05-1x106 cm-3) Denser and colder gas component à On the verge of star formation? ⋆"from non-LTE analysis (RADEX, van der Tak+2007) Laura Colzi Vrad (km s-1)Vrad (km s-1) Ta* (K) Ta* (K) NON-LTE analysis
Laura Colzi Excitation and spatial study towards G+0.693
Laura Colzi Excitation and spatial study towards G+0.693 70-85 km s-1 Single pixels (0.18 pc) FWHM 1.3 –4.9 km s-1 Colzi et al. (2024), A&A, 690, A121
Laura Colzi Excitation and spatial study towards G+0.693 C2 will not fragment and possibly expand C3 can either collapse or further fragment 70-85 km s-1 Single pixels (0.18 pc) FWHM 1.3 –4.9 km s-1 Colzi et al. (2024), A&A, 690, A121
CONCLUSIONS BROAD COMPONENT NARROW COMPONENT COSMIC D/H = 2.55 x 10-5 Our data suggested the presence of a prestellar condensation in the Central Molecular Zone (CMZ) that might be on the verge of the collapse Colzi et al. (2022a,2024) Laura Colzi C3 80-85 km s-1 70-75 vs 80-85 km s-1 C3 C2 C2
Chemical Signatures of a prestellar cluster in the Galactic Center Laura Colzi (Centro de Astrobiología, CSIC-INTA) March 10th 2025 J. Martín-Pintado, S. Zeng, I. Jiménez-Serra,V. M. Rivilla, Sanz-Novo, M. and many others... Grant PID2022-136814NB-I00 funded by:
BACK UP SLIDES
ACES ALMA LARGE PROGRAM Inner 100 pc of the CMZ covered at 1.5’’ (0.05 pc) of resolution in Band 3 Total time allocation: 112 hrs (12m) + 7m and TP from the largest scales (12m+7m+TP) to individual cores (~1.5’’à0.05 pc) Laura Colzi Main PI: Steven Longmore
WP3: Chemistry and Physical Modeling Goals Determination of the physical and chemical properties of the dust, molecular gas and ionized gas structures mapped with ACES from the largest scales (12m+7m+TP) to individual cores (~1.5’’à0.06 pc) Laura Colzi and Izaskun Jiménez-Serra (Centro de Astrobiología, CSIC-INTA) Contact us @: [email protected] [email protected]-csic.es
Spectral Setup and Molecules Covered Credits: Elisabeth Mills Laura Colzi Dense gas tracers (HCO+, HCN, CS) Shock tracers (SiO, HNCO, SO) PDR tracers (HCO) Ionized gas (H40a) Hot cores (HC3N*, COMs) 6 spectral windows:
A first example: mm1 and mm2 (hot)cores in Sgr C Laura Colzi Molecules identified so far towards mm1: HC15N, HN13C, H13CN,HC3N (cyanoacetylene), HC13CCN, HCC13CN, H13CO+,HCO+, HN13CO, HNCO (isocyanic acid), CS, SO, 34SO,SiO,HC5N (cyanodiacetylene), C2H5CN (proprionitrile), H2CCO (ketene), CCS, NH2CN (cyanamide), CH3OCHO (methyl formate), C2H5OH (ethanol), CH3OCH3(dimethyl ether), CH3SH (methanethiol or methyl mercaptan), CH3NCO (methyl isocyanate), CH3CHO (acetaldehyde), H2CO (formaldehyde), CH3OH (methanol), HC3N v6=1, v7=1, HC3N v7=2, HC(O)NH2(formamide), CH318OH
70-80 km s-1 40-50 km s-1 50-60 km s-1 60-70 km s-1 Hole Massive cloud Shell Massive cloud Laura Colzi Excitation and spatial study towards G+0.693 HNCO(40,4-30,3) IRAM 30m MAPS 10 pc See also Hasegawa+1994; Sato+2000; Zeng+2020; Armijos-Abendaño+2020; Enokiya & Fukui 2022 Colzi et al. (2024), A&A, 690, A121
Beyond our Galaxy… Laura Colzi Galaxy NGC 253 Butterworth, J., .., Colzi, L., et al.: A&A, 693, A65 (2025)