Energetic galaxy-wide outflows in high-redshift ultra-luminous infrared galaxies hosting AGN activity (1205.1801v3)

Abstract: We present integral field spectroscopy observations, covering the [O III]4959,5007 emission-line doublet of eight high-redshift (z=1.4-3.4) ultra-luminous infrared galaxies (ULIRGs) that host Active Galactic Nuclei (AGN) activity, including known sub-millimetre luminous galaxies (SMGs). The targets have moderate radio luminosities that are typical of high-redshift ULIRGs (L(1.4GHz)=10^24-10^25W/Hz) and therefore are not radio-loud AGN. We de-couple kinematic components due to the galaxy dynamics and mergers from those due to outflows. We find evidence in the four most luminous systems (L([O III])>~10^43erg/s) for the signatures of large-scale energetic outflows: extremely broad [O III] emission (FWHM ~ 700-1400km/s) across ~4-15kpc, with high velocity offsets from the systemic redshifts (up to ~850km/s). The four less luminous systems have lower quality data displaying weaker evidence for spatially extended outflows. We estimate that these outflows are potentially depositing energy into their host galaxies at considerable rates (~10^43-10^45erg/s); however, due to the lack of constraints on the density of the outflowing material and the structure of the outflow, these estimates should be taken as illustrative only. Based on the measured maximum velocities (v(max)~400-1400km/s) the outflows observed are likely to unbind some fraction of the gas from their host galaxies, but are unlikely to completely remove gas from the galaxy haloes. By using a combination of energetic arguments and a comparison to ULIRGs without clear evidence for AGN activity, we show that the AGN activity could be the dominant power source for driving all of the observed outflows, although star formation may also play a significant role in some of the sources.

Analysis of Energetic Galactic Outflows in High-Redshift ULIRGs with AGN Activity

The paper presented in this paper focuses on the investigation of galaxy-wide outflows in high-redshift Ultra-Luminous Infrared Galaxies (ULIRGs), particularly those that host Active Galactic Nuclei (AGN) activity. Such investigations are crucial as they examine the evolutionary mechanics underlying massive galaxies, providing empirical support to theoretical models of galaxy formation and evolution. The research employs integral field unit (IFU) spectroscopy to observe ionized gas properties, revealing insights into the kinematics and dynamics of these distant astronomical entities.

The primary objective in conducting this research is to ascertain the presence and scale of outflows in high-redshift ULIRGs with AGN activity. Thereby, the researchers aim to provide evidence of AGN activity's role in driving outflows, further understanding the influence of these phenomena on the host galaxies' evolution.

Key Findings and Results

1. Outflow Characteristics: The data shows broad [O III] emission lines indicating outflows with widths ranging from 700 to 1400 km s$^-1$, extending up to 15 kpc from the galaxy center and exhibiting high velocity offsets up to 850 km s$^-1$. These features compel a revisitation of how gas dynamics within ULIRGs function, especially regarding how AGN can modulate such dynamics.
2. Presence of AGN: The paper suggests the AGN activity could be instrumental in generating the observed outflows, although high star formation rates might also contribute. Nonetheless, the velocity offsets and spatial extent of the observed outflows imply that the AGN activity stands as a significant or even dominant driving force in many cases.
3. Energetic Implications: The researchers estimated energy injection rates into the interstellar medium (ISM) as approximately 10$^44$ to 10$^45$ erg s$^-1$. This infusion of kinetic energy is critical for understanding the feedback mechanisms that could potentially stifle gas accretion onto the central black holes and regulate star formation within the host galaxy.
4. Potential to Unbind Gas: While the findings suggest outflows are capable of unbinding some fraction of gas from the host galaxy, their ability to entirely remove it from the galaxy's halo is less certain. However, the paper provides a valuable quantitative treatment of outflow velocities and associated energy scales.
5. Observational Comparisons and Future Implications: The comparison of IFU observations with models of high-redshift submillimeter galaxies (SMGs) further solidifies the crucial role AGN outflows play in galaxy evolution narratives. The insights presented contribute to a growing repository of evidence essential for formulating refined astrophysical models corresponding to the early universe.

Broader Implications

This paper importantly places stringent constraints on models of galaxy evolution necessitating AGN-driven feedback mechanisms. By mapping out the kinematic landscape of high-redshift galaxies, it echoes the need for simulations to incorporate AGN feedback accurately across various cosmic epochs. The quantitative portrayal of outflow energy mechanics offers critical parameters for such models, emphasizing the intersection of empirical astrophysics with theoretical astrophysical model building.

Future Directions

This research advocates for deepened inquiry into the multi-faceted nature of galactic outflows, advocating for improved resolution in IFU spectroscopy to further delineate the intricate structure and dynamics of gas in high-redshift galaxies. Expanding the sample size and observational baseline could yield more statistically robust results, fortifying the relationship between AGN activity and larger galactic feedback processes.

Overall, this work enhances our grasp of how early massive galaxies evolve, underlining AGN-driven outflows as a keystone element in regulating these processes. Further exploration could potentially unfold more comprehensive insights into the architecture of modern-day galaxy clusters, building upon the foundation laid by studies like this one.