IRAS 09104+4109

IRAS 09104+4109 is a galaxy located in the constellation Lynx. With a redshift of 0.440797, the light travel time for this galaxy, corresponds to 4.8 billion light-years from Earth. It is the brightest cluster galaxy in CDGS 25, also known as WHL J091345.5+405628 and a notable, unique ultraluminous infrared galaxy.

Features
IRAS 09104+4109 has an active galactic nucleus (AGN). It is a Seyfert type 2 galaxy with a strong emission-line spectrum (z = 0.442), with a range of excitations and very large equivalent widths but shows no broad lines. Moreover, IRAS 09104+4109 is classified a cD galaxy located inside a cool rich cluster of galaxies, experiencing a cooling flow. The galaxy is the most luminous object to be discovered by IRAS survey, emitting 6 x 10^12^ L_sun_ h^-2^, which 99% of the energy emerges at infrared wavelengths. The high luminosity of IRAS 09104+4109 might be related to an interaction with one or more members of the rich cluster in which it lies. It is selected by its strong 60 m emission (>0.5 Jy), yet faint optical magnitude (V>18).

The galaxy shows a "warm" far-IR color F(25 m)/F(60 m) of 0.3, similar to of luminous optically selected quasars and suggests that much of the far-IR emission is emitted from dust heated by the central ultraviolet (UV) continuum source. The rest frame of UV/optical spectrum of the nucleus shows a type 2 spectrum with strong, narrow emission lines covering a range of ionizations. This implies photoionization by a strong UV nonthermal continuum.

IRAS 09104+4109 has a luminosity bolometer of ~ 1012.6 h-2 L sun, which its optical spectrum is characterized by the presence of narrow emission lines, although broad Balmer and Mg II lines were observed in polarized light. These findings, found there is a quasar inside IRAS 09104+4109, ionizing the narrow-line region and heats dust within ~130 pc of its central engine. Furthermore, IRAS 09104+4109 produces a radio jet.

A study conducted in 2007, proves IRAS 09104+4109 as the first "changing-look quasar". This was done by having researchers to analyze the spectroscopic data from the PN and the MOS cameras in the 0.4–10 keV band. They also used an archival BeppoSAX 1–50 keV observation of to investigate the possible variations of the quasar emission and found that the X-ray emission in the EPIC band is dominated by the intra-cluster medium thermal emission, which the quasar contributes ~35% of the total flux in the 2–10 keV band.

Further studies in 2012, showed that IRAS 09104+4109 is a rare example of a dust enshrouded quasar which also associated with a double-lobed radio source at the position angle of =333° (probably an FR II radio source). However, the steep radio spectral index and misalignment between the jets and ionized optical emission suggested that the orientation of the quasar in IRAS 09104+4109 had recently changed. To prove this hypothesis, researchers used a combination of new, multiband Giant Metrewave Radio Telescope observations and archival radio data and confirmed that the jets in IRAS 09104+ 4109, estimated to 20-160 Myr, are no longer actively fed by energetic particles. This results suggested that the realignment of the quasar, the cessation of jet activity and the onset of rapid star formation in IRAS 09104+4109, may have been caused by a gas-rich galaxy merger.

A Northern Extended Millimeter Array (NOEMA) found there are traces of carbon oxide (2–1) in the z=0.4418 cluster-central IRAS 09104+4109, which ~4.5x10^10 M sol of molecular gas is found, in and around the galaxy. As in many low redshift cool core clusters, the gas is located in a series of clumps extending along the old radio jets and lobes. It has a relatively low velocity dispersion of (336 [+39,-35] km/s FWHM) and shows no velocity gradients indicative of outflow or infall. Roughly, half its gas is located in a central clump on the northeast side of the galaxy, overlapping a bright ionized gas filament and a spur of excess X-ray emission, suggesting that this is a location of rapid cooling. The molecular gas is unusually extended, outwards to ~55 kpc radius, which is comparable to the scale of the filamentary nebula in the Perseus cluster, the higher redshift of this system. The extent falls within the thermal instability radius of the intracluster medium (ICM), with t cool/t_ff<25 and t_cool}/t_eddy~1 within ~70 kpc. Continuum measurements at 159.9 GHz from NOEMA and 850 micron from the JCMT SCUBA-2 show excess far infrared emission, which we interpret as free-free emission arising from the ongoing starburst. These observations suggest that the ICM cooling is not strongly affected by its buried quasar, and that cooling from the ICM can build gas reservoirs sufficient enough, to fuel the quasar-mode activity and drive the reorientation of its central AGN.