Periodic Reporting for period 4 - HIDDeN (HIDDeN - Exploring the Hidden Dusty Nuclei of Galaxies)
Periodo di rendicontazione: 2023-04-01 al 2025-03-31
Luminous infrared galaxies (LIRGs) are the nearby Universe’s test beds for the most intense episodes of galaxy and black-hole growth: more than 90 % of their energy emerges in the far-infrared from dust-enshrouded starbursts and/or growing super-massive black holes (SMBHs). The very nuclei where this activity unfolds are often Compton-thick—opaque even to hard X-rays—so the mechanisms that funnel gas in, ignite feedback, and assemble bulges and SMBHs remain largely hidden. Unlocking this phase is essential if we are to complete the timeline of cosmic evolution. HIDDeN — Exploring the HIdden Dusty Nuclei of Galaxies removed that veil. Leveraging millimetre and sub-millimetre spectroscopy with ALMA, NOEMA and partner facilities, the project aimed to:
1.Map vibrationally-excited molecular tracers that pinpoint deeply buried AGNs;
2. Image molecular inflows and outflows to measure how efficiently gas is accreted, expelled and recycled
3. Study the starburst-AGN connection to find if SMBHs and nuclear stellar populations grow in concert
4. Extend these diagnostics out to redshift z ≈ 1–2—the “high-noon” epoch of galaxy growth—to probe obscured evolution across cosmic time.
These data aimed to quantify the duty-cycle of hidden SMBH accretion, reveal how feedback regulates star formation, and refine models of galaxy–black-hole co-evolution.
Understanding how galaxies assemble and self-regulate resonates far beyond astronomy: it satisfies a universal human quest to know our origins and drives innovation in receiver technology, high-frequency data processing and big-data analytics—capabilities that underpin modern communication, navigation and climate monitoring. By exposing the “dark hearts” of galaxies, HIDDeN not only filled a crucial gap in astrophysics but also inspires future scientists and reminds society of its shared cosmic heritage.
1.Map vibrationally-excited molecular tracers that pinpoint deeply buried AGNs;
2. Image molecular inflows and outflows to measure how efficiently gas is accreted, expelled and recycled
3. Study the starburst-AGN connection to find if SMBHs and nuclear stellar populations grow in concert
4. Extend these diagnostics out to redshift z ≈ 1–2—the “high-noon” epoch of galaxy growth—to probe obscured evolution across cosmic time.
These data aimed to quantify the duty-cycle of hidden SMBH accretion, reveal how feedback regulates star formation, and refine models of galaxy–black-hole co-evolution.
Understanding how galaxies assemble and self-regulate resonates far beyond astronomy: it satisfies a universal human quest to know our origins and drives innovation in receiver technology, high-frequency data processing and big-data analytics—capabilities that underpin modern communication, navigation and climate monitoring. By exposing the “dark hearts” of galaxies, HIDDeN not only filled a crucial gap in astrophysics but also inspires future scientists and reminds society of its shared cosmic heritage.
Luminous infrared galaxies (LIRGs) are nearby laboratories for extreme galaxy and black-hole growth, yet their power-houses are buried behind optically thick dust. The HIDDeN project lifted that veil.
Work performed We secured the large ALMA programmes CONquest and follow-up CONfirm, plus complementary APEX, NOEMA, VLA, eMERLIN, VLBI, JWST and VLT/MUSE observations. Vibrationally-excited HCN (HCN-vib) was used as a torch to map 38 U/LIRGs at 0.1–0.3″ (15–50 pc) resolution, with sub-10 pc imaging of IC 860, NGC 1377, Zw049, IRAS17578, ESO-173 and ESO320. A parallel redshift survey extended the method to z ≈ 4.
Main results
• Incidence of buried nuclei – Compact Obscured Nuclei (CONs) are four times more common than assumed; 40 % of the most luminous ULIRGs host a CON.
• Feeding and feedback – CONs show simultaneous radial inflows and radio-quiet, collimated molecular outflows (CMOs). In IC 860 the inflow hides the outflow; in NGC 1377 a 2 pc-wide rotating molecular jet appears without a radio jet, revealing a new feedback channel.
• Launch regions of coutflows: HIDDeN used cutting-edge ALMA capacity to pinpont the nuclear launch regions of the powerful molecular outflows – a key point in determining their nature
• Dense-gas diagnostics – HCN-vib luminosity, coronal free–free emission and mm-continuum slopes were calibrated as quantitative tracers of deeply buried AGN power and used to discover the most distant CON-like object yet (z = 3.9).
• AGN leakage – MUSE [O III] imaging of NGC 4418 uncovered ionised knots beyond the opaque core, showing that even the deepest nuclei can leak ionising photons.
Exploitation and dissemination Although the work is fundamental, the new mm/sub-mm diagnostics, receiver set-ups and analysis pipelines are already being adopted by the ALMA community and folded into JWST planning tools, enhancing future high-redshift surveys. Our coronal model and observational techniques are shared with the community. Results were shared through >30 refereed papers >35 conference talks, several invited keynotes and >six dedicated workshops. Outreach included public lectures, and interviews for Swedish Radio P4, Vetenskapsradion, Sveriges Television and the PI was featured on SRs Söndagsintervjun – a very rare forum for a scientist.
HIDDeN therefore delivers the first statistically robust view of the hidden growth phase linking starbursts and super-massive black-hole accretion and establishes observational benchmarks that will guide ALMA, VLBI, SKA and JWST science in the coming decade.
Work performed We secured the large ALMA programmes CONquest and follow-up CONfirm, plus complementary APEX, NOEMA, VLA, eMERLIN, VLBI, JWST and VLT/MUSE observations. Vibrationally-excited HCN (HCN-vib) was used as a torch to map 38 U/LIRGs at 0.1–0.3″ (15–50 pc) resolution, with sub-10 pc imaging of IC 860, NGC 1377, Zw049, IRAS17578, ESO-173 and ESO320. A parallel redshift survey extended the method to z ≈ 4.
Main results
• Incidence of buried nuclei – Compact Obscured Nuclei (CONs) are four times more common than assumed; 40 % of the most luminous ULIRGs host a CON.
• Feeding and feedback – CONs show simultaneous radial inflows and radio-quiet, collimated molecular outflows (CMOs). In IC 860 the inflow hides the outflow; in NGC 1377 a 2 pc-wide rotating molecular jet appears without a radio jet, revealing a new feedback channel.
• Launch regions of coutflows: HIDDeN used cutting-edge ALMA capacity to pinpont the nuclear launch regions of the powerful molecular outflows – a key point in determining their nature
• Dense-gas diagnostics – HCN-vib luminosity, coronal free–free emission and mm-continuum slopes were calibrated as quantitative tracers of deeply buried AGN power and used to discover the most distant CON-like object yet (z = 3.9).
• AGN leakage – MUSE [O III] imaging of NGC 4418 uncovered ionised knots beyond the opaque core, showing that even the deepest nuclei can leak ionising photons.
Exploitation and dissemination Although the work is fundamental, the new mm/sub-mm diagnostics, receiver set-ups and analysis pipelines are already being adopted by the ALMA community and folded into JWST planning tools, enhancing future high-redshift surveys. Our coronal model and observational techniques are shared with the community. Results were shared through >30 refereed papers >35 conference talks, several invited keynotes and >six dedicated workshops. Outreach included public lectures, and interviews for Swedish Radio P4, Vetenskapsradion, Sveriges Television and the PI was featured on SRs Söndagsintervjun – a very rare forum for a scientist.
HIDDeN therefore delivers the first statistically robust view of the hidden growth phase linking starbursts and super-massive black-hole accretion and establishes observational benchmarks that will guide ALMA, VLBI, SKA and JWST science in the coming decade.
HIDDeN has pushed observational astrophysics beyond the state-of-the-art by opening a direct window on the deeply buried power-sources of luminous infrared galaxies (LIRGs). Using the Atacama Large Millimetre/sub-millimetre Array (ALMA) we executed the first volume-limited CONquest survey, exploiting vibrationally-excited HCN as a uniquely sensitive tracer of compact obscured nuclei (CONs). This diagnostic couples to the intense dust-reprocessed infrared radiation field and re-emits it at millimetre wavelengths, revealing energy sources invisible even to hard X-rays.
Key advances
• Frequency of extreme obscuration – CONquest shows that ~40 % of ultra-luminous systems and one quarter of all local LIRGs host CONs—higher than the expected fraction.
• Parsec-scale physics – Follow-up CONfirm imaging at 0.02–0.05″ resolves gas inflows, collimated molecular outflows and rotating disks, delivering the first dynamical-mass estimates for fully embedded super-massive black holes. We discovered a radio-quiet molecular jet in NGC 1377, mapped its launch structure, and proved that inflowing gas in IC 860 can mask its own outflow, clarifying the hidden feeding/feedback loop.
• New diagnostics – ALMA/NOEMA data combined with novel radiative-transfer models disentangle free-free coronal emission from dust, allowing the bolometric power of buried AGNs to be measured where X-rays fail; the toolbox is already being applied to high-redshift galaxies and has revealed vigorous HCN-vib emission at z ≈ 3.9.
• Multi-wavelength breakthroughs – VLT-MUSE maps show that ionising photons leak through 1000 mag of extinction, creating [O III] knots hundreds of parsecs away—overturning the view that CONs are completely sealed. JWST imaging finds vigorous but patchy star formation around nuclei of non-CON LIRGs while young nuclear star formation of CONs seem not to be prominent (or is being free-free suppressed).
Legacy
We have released calibrated data cubes, catalogues for the use of the community, and the coronal-emission code will be made available to researcher, ensuring immediate uptake by the ALMA/JWST community and by forthcoming surveys with the SKA, VLBI, ngVLA and ELT. HIDDeN therefore establishes the benchmark technique and reference sample for identifying and characterising the most heavily obscured phases of galaxy and black-hole growth.
Glossary:
Atacama Large mm/submm Array=ALMA
Atacama Pathfinder EXperiment=APEX
NOrthern Extended Millimeter ARRAY=NOEMA
VLA=Very Large Array
VLBI=Very Long Baseline Interferometry
EVN=European VLBI Network
JWST= James Webb Space Telescope
MUSE=The Multi Unit Spectroscopic Explorer
HST= Hubble Space Telescope
Key advances
• Frequency of extreme obscuration – CONquest shows that ~40 % of ultra-luminous systems and one quarter of all local LIRGs host CONs—higher than the expected fraction.
• Parsec-scale physics – Follow-up CONfirm imaging at 0.02–0.05″ resolves gas inflows, collimated molecular outflows and rotating disks, delivering the first dynamical-mass estimates for fully embedded super-massive black holes. We discovered a radio-quiet molecular jet in NGC 1377, mapped its launch structure, and proved that inflowing gas in IC 860 can mask its own outflow, clarifying the hidden feeding/feedback loop.
• New diagnostics – ALMA/NOEMA data combined with novel radiative-transfer models disentangle free-free coronal emission from dust, allowing the bolometric power of buried AGNs to be measured where X-rays fail; the toolbox is already being applied to high-redshift galaxies and has revealed vigorous HCN-vib emission at z ≈ 3.9.
• Multi-wavelength breakthroughs – VLT-MUSE maps show that ionising photons leak through 1000 mag of extinction, creating [O III] knots hundreds of parsecs away—overturning the view that CONs are completely sealed. JWST imaging finds vigorous but patchy star formation around nuclei of non-CON LIRGs while young nuclear star formation of CONs seem not to be prominent (or is being free-free suppressed).
Legacy
We have released calibrated data cubes, catalogues for the use of the community, and the coronal-emission code will be made available to researcher, ensuring immediate uptake by the ALMA/JWST community and by forthcoming surveys with the SKA, VLBI, ngVLA and ELT. HIDDeN therefore establishes the benchmark technique and reference sample for identifying and characterising the most heavily obscured phases of galaxy and black-hole growth.
Glossary:
Atacama Large mm/submm Array=ALMA
Atacama Pathfinder EXperiment=APEX
NOrthern Extended Millimeter ARRAY=NOEMA
VLA=Very Large Array
VLBI=Very Long Baseline Interferometry
EVN=European VLBI Network
JWST= James Webb Space Telescope
MUSE=The Multi Unit Spectroscopic Explorer
HST= Hubble Space Telescope