About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs

Mischa Schirmer, Sangeeta Malhotra, Nancy A. Levenson, Hai Fu, Rebecca L. Davies, William C. Keel, Paul Torrey, Vardha N. Bennert, Anna Pancoast, James E H Turner

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

We report the discovery of 14 Lyα blobs (LABs) at z ~ 0.3, existing at least 4-7 billion years later in the Universe than all other LABs known. Their optical diameters are 20-70 kpc, and GALEX data imply Lyα luminosities of (0.4-6.3) × 1043 erg s-1. Contrary to high-z LABs, they live in low-density areas. They are ionized by AGN, suggesting that cold accretion streams as a power source must deplete between z = 2 and 0.3. We also show that transient AGN naturally explain the ionization deficits observed in many LABs. Their Lyα and X-ray fluxes decorrelate below ≲106 years because of the delayed escape of resonantly scattering Lyα photons. High Lyα luminosities do not require currently powerful AGN, independent of obscuration. Chandra X-ray data reveal intrinsically weak AGN, confirming the luminous optical nebulae as impressive ionization echoes. For the first time, we also report mid-infrared thermal echoes from the dusty tori. We conclude that the AGN have faded by three to four orders of magnitude within the last 104-5 years, leaving fossil UV, optical and thermal radiation behind. The host galaxies belong to the group of previously discovered Green Bean galaxies (GBs). Gemini optical imaging reveals smooth spheres, mergers, spectacular outflows and ionization cones. Because of their proximity and high flux densities, GBs are perfect targets to study AGN feedback, mode switching and the Lyα escape. The fully calibrated, co-added optical FITS images are publicly available.

Original languageEnglish (US)
Article numberstw1819
Pages (from-to)1554-1586
Number of pages33
JournalMonthly Notices of the Royal Astronomical Society
Volume463
Issue number2
DOIs
StatePublished - Dec 1 2016

Fingerprint

echoes
ionization
escape
luminosity
galaxies
occultation
thermal radiation
fossils
radiation
nebulae
erg
merger
proximity
cones
x rays
outflow
flux density
universe
accretion
scattering

Keywords

  • Galaxies: active
  • Galaxies: evolution
  • Radiative transfer
  • Ultraviolet: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Schirmer, M., Malhotra, S., Levenson, N. A., Fu, H., Davies, R. L., Keel, W. C., ... Turner, J. E. H. (2016). About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs. Monthly Notices of the Royal Astronomical Society, 463(2), 1554-1586. [stw1819]. https://doi.org/10.1093/mnras/stw1819

About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs. / Schirmer, Mischa; Malhotra, Sangeeta; Levenson, Nancy A.; Fu, Hai; Davies, Rebecca L.; Keel, William C.; Torrey, Paul; Bennert, Vardha N.; Pancoast, Anna; Turner, James E H.

In: Monthly Notices of the Royal Astronomical Society, Vol. 463, No. 2, stw1819, 01.12.2016, p. 1554-1586.

Research output: Contribution to journalArticle

Schirmer, M, Malhotra, S, Levenson, NA, Fu, H, Davies, RL, Keel, WC, Torrey, P, Bennert, VN, Pancoast, A & Turner, JEH 2016, 'About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs', Monthly Notices of the Royal Astronomical Society, vol. 463, no. 2, stw1819, pp. 1554-1586. https://doi.org/10.1093/mnras/stw1819
Schirmer, Mischa ; Malhotra, Sangeeta ; Levenson, Nancy A. ; Fu, Hai ; Davies, Rebecca L. ; Keel, William C. ; Torrey, Paul ; Bennert, Vardha N. ; Pancoast, Anna ; Turner, James E H. / About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs. In: Monthly Notices of the Royal Astronomical Society. 2016 ; Vol. 463, No. 2. pp. 1554-1586.
@article{6c1d9974415342269f1efb08964e3dd7,
title = "About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs",
abstract = "We report the discovery of 14 Lyα blobs (LABs) at z ~ 0.3, existing at least 4-7 billion years later in the Universe than all other LABs known. Their optical diameters are 20-70 kpc, and GALEX data imply Lyα luminosities of (0.4-6.3) × 1043 erg s-1. Contrary to high-z LABs, they live in low-density areas. They are ionized by AGN, suggesting that cold accretion streams as a power source must deplete between z = 2 and 0.3. We also show that transient AGN naturally explain the ionization deficits observed in many LABs. Their Lyα and X-ray fluxes decorrelate below ≲106 years because of the delayed escape of resonantly scattering Lyα photons. High Lyα luminosities do not require currently powerful AGN, independent of obscuration. Chandra X-ray data reveal intrinsically weak AGN, confirming the luminous optical nebulae as impressive ionization echoes. For the first time, we also report mid-infrared thermal echoes from the dusty tori. We conclude that the AGN have faded by three to four orders of magnitude within the last 104-5 years, leaving fossil UV, optical and thermal radiation behind. The host galaxies belong to the group of previously discovered Green Bean galaxies (GBs). Gemini optical imaging reveals smooth spheres, mergers, spectacular outflows and ionization cones. Because of their proximity and high flux densities, GBs are perfect targets to study AGN feedback, mode switching and the Lyα escape. The fully calibrated, co-added optical FITS images are publicly available.",
keywords = "Galaxies: active, Galaxies: evolution, Radiative transfer, Ultraviolet: galaxies",
author = "Mischa Schirmer and Sangeeta Malhotra and Levenson, {Nancy A.} and Hai Fu and Davies, {Rebecca L.} and Keel, {William C.} and Paul Torrey and Bennert, {Vardha N.} and Anna Pancoast and Turner, {James E H}",
year = "2016",
month = "12",
day = "1",
doi = "10.1093/mnras/stw1819",
language = "English (US)",
volume = "463",
pages = "1554--1586",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "2",

}

TY - JOUR

T1 - About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs

AU - Schirmer, Mischa

AU - Malhotra, Sangeeta

AU - Levenson, Nancy A.

AU - Fu, Hai

AU - Davies, Rebecca L.

AU - Keel, William C.

AU - Torrey, Paul

AU - Bennert, Vardha N.

AU - Pancoast, Anna

AU - Turner, James E H

PY - 2016/12/1

Y1 - 2016/12/1

N2 - We report the discovery of 14 Lyα blobs (LABs) at z ~ 0.3, existing at least 4-7 billion years later in the Universe than all other LABs known. Their optical diameters are 20-70 kpc, and GALEX data imply Lyα luminosities of (0.4-6.3) × 1043 erg s-1. Contrary to high-z LABs, they live in low-density areas. They are ionized by AGN, suggesting that cold accretion streams as a power source must deplete between z = 2 and 0.3. We also show that transient AGN naturally explain the ionization deficits observed in many LABs. Their Lyα and X-ray fluxes decorrelate below ≲106 years because of the delayed escape of resonantly scattering Lyα photons. High Lyα luminosities do not require currently powerful AGN, independent of obscuration. Chandra X-ray data reveal intrinsically weak AGN, confirming the luminous optical nebulae as impressive ionization echoes. For the first time, we also report mid-infrared thermal echoes from the dusty tori. We conclude that the AGN have faded by three to four orders of magnitude within the last 104-5 years, leaving fossil UV, optical and thermal radiation behind. The host galaxies belong to the group of previously discovered Green Bean galaxies (GBs). Gemini optical imaging reveals smooth spheres, mergers, spectacular outflows and ionization cones. Because of their proximity and high flux densities, GBs are perfect targets to study AGN feedback, mode switching and the Lyα escape. The fully calibrated, co-added optical FITS images are publicly available.

AB - We report the discovery of 14 Lyα blobs (LABs) at z ~ 0.3, existing at least 4-7 billion years later in the Universe than all other LABs known. Their optical diameters are 20-70 kpc, and GALEX data imply Lyα luminosities of (0.4-6.3) × 1043 erg s-1. Contrary to high-z LABs, they live in low-density areas. They are ionized by AGN, suggesting that cold accretion streams as a power source must deplete between z = 2 and 0.3. We also show that transient AGN naturally explain the ionization deficits observed in many LABs. Their Lyα and X-ray fluxes decorrelate below ≲106 years because of the delayed escape of resonantly scattering Lyα photons. High Lyα luminosities do not require currently powerful AGN, independent of obscuration. Chandra X-ray data reveal intrinsically weak AGN, confirming the luminous optical nebulae as impressive ionization echoes. For the first time, we also report mid-infrared thermal echoes from the dusty tori. We conclude that the AGN have faded by three to four orders of magnitude within the last 104-5 years, leaving fossil UV, optical and thermal radiation behind. The host galaxies belong to the group of previously discovered Green Bean galaxies (GBs). Gemini optical imaging reveals smooth spheres, mergers, spectacular outflows and ionization cones. Because of their proximity and high flux densities, GBs are perfect targets to study AGN feedback, mode switching and the Lyα escape. The fully calibrated, co-added optical FITS images are publicly available.

KW - Galaxies: active

KW - Galaxies: evolution

KW - Radiative transfer

KW - Ultraviolet: galaxies

UR - http://www.scopus.com/inward/record.url?scp=84996520563&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84996520563&partnerID=8YFLogxK

U2 - 10.1093/mnras/stw1819

DO - 10.1093/mnras/stw1819

M3 - Article

AN - SCOPUS:84996520563

VL - 463

SP - 1554

EP - 1586

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 2

M1 - stw1819

ER -